All in One SEO Pack
There are a lot of ways for your website to get seen and while WordPress has become the most popular platform for small business owners to create great content they need all the help they can get. The All in One SEO Pack is a way to help level the playing field a little. In combination with keyword suggestion tools this plugin helps create site wide and post specific keywords that help search engines zero in on content that can lead to networking opportunities and potential leads/sales conversions. With more than 7,331,902 downloads and counting this plugin is a absolute must in any online marketing effort no matter what size your business.
http://wordpress.org/extend/plugins/all-in-one-seo-pack

cformsII
Cforms is a great plugin for creating all kinds of different forms for potential customers looking to get more information about a product or service you are selling. It comes with some generic templates that are easily adaptable to any WordPress theme or the option to experiment with the built in Cascading Style Sheet (CSS) wizard to manipulate the look of the form for the site. Some of my favorite features is that you can clone your forms without having to start from scratch, start and stop dates if you are running a marketing campaign, built-in CAPTCHA security questions to keep the bots at bay, and much more. I would say that this plugin is just as feature rich as any of the popular commercial email opt-in/newsletters out there.
http://www.deliciousdays.com/cforms-plugin

Digg Digg
If you want your content to be seen by members of your tribe another great tool is Digg Digg. Digg Digg makes it easy for your viewers to share your content via popular social media networks like Twitter and Facebook with others in their tribe. This is one of the reasons the leading internet marketing magazine, Mashable, became so popular at the beginning of the new media revolution. They realized the power of shareability and combined with great content, how to make it go viral. I recommend Digg Digg for anybody looking to extend the reach of people seeing of their content.
http://www.mkyong.com/blog/digg-digg-wordpress-plugin

Google XML Sitemaps
This is probably the least visible of the plugins on my list, but probably one of the most important when getting your website indexed properly by Google or other search engines. Once you have gotten your WordPress website setup the way you like it an can focus on creating good content signup for a Google webmaster tools account and submit the link of your XML sitemap and it will help Google and other search engines you submit to correctly crawl your website thus increasing page ranking in combination with your organic SEO efforts and social network sharing. When you add this to your Google Webmasters tools it takes a couple days for the site to get indexed, but once it does it spits our a lot of helpful information on improving your page rankings with other analytic dashboard reporting like Google Analytics.
http://www.arnebrachhold.de/projects/wordpress-plugins/google-xml-sitemaps-generator

LinkWithin
I am horrible with figuring out how to set up a related posts with another WordPress plugin called, Yet Another Related Post Plugin and someday I may revisit it, but for now LinkWithin is a great plugin for bloggers to give the reader thumbnailed pictures and post titles at the top or bottom of a blog post. This plugin helps combat the a content producer’s biggest challenge and that is to keep the attention of the viewer because these days eyeballs have a lot of different choices and if you can get past the average 7 sec. attention span with quality copy and video then you lower the bounce rate from a unique visitors first visit to your website.
http://www.linkwithin.com/learn

Quick Cache
In the words of Keanu Reeves in his countless action movies, “Waoooh.” Speed was good, but when they took it on the water and jumped the shark it was over. Good thing Quick Cache hasn’t gone down that same path. Viewers like fast websites because we have become a society of instant satisfaction and shouldn’t have to wait for a website to load. What most people don’t know is that while it maybe seen as a single issue there are a lot of factors that go into making a website slow or fast. Besides internet connections, speed of the web and database servers, shared, virtual, or cloud, etc. Quick Cache takes a real-time snapshot ( building a cache ) of every Page, Post, Category, Link, etc. These snapshots are then stored ( cached ) intuitively, so they can be referenced later, in order to save all of that processing time that has been dragging your site down which ultimately leads to lost revenue.
http://www.primothemes.com/post/product/quick-cache-plugin-for-wordpress/

SEO Slugs
SEO Slugs is a simple plugin, but it helps get rid of common words like “what”, “you” or “can” out of your post slug to make it more search engine friendly. It is a simple yet effective plugin, but a must have for any SEO arsenal.
http://wordpress.org/extend/plugins/seo-slugs

WPtouch
If a blog needed at least 25 pieces of flair this plugin would probably be #1 on the list. For me it is a guilty please because I am a fan of making things mobile from a graphic usability perspective. WPtouch essentially turns your WordPress blog into a mobile application so it is easier to navigate your website from a smartphone or tablet device. Once again this like the other plugins I have mentioned above WPtouch literally touches on efficiency from the end users point of view. This extends viewership, time spent on the website, and sharebility.
https://www.bravenewcode.com/store/plugins/wptouch-pro

WordPress.com Stats
While Google Analytics is probably the best analytics tool for evaluating the traffic to your website the plugins for WordPress are a little lacking when it comes to integrating the results in the WordPress dashboard. WordPress.com Stats does a great job of having an integrated reporting heads up display (HUD) of top referrers, pages visited, and my favorite, search engine terms that people used to find your website. This helps give you some insight on what you are doing right and areas of content creation and SEO and Social Media Marketing you can do better.
http://wordpress.org/extend/plugins/stats

Updraft – Backup/Restore
Working at a web hosting company every once and awhile I will get a customer upset that we only provide a 2 copies of their websites on a two week cycle. My response to them is that on current hardware their is limitations with regards to space and that we are moving to an environment where we can take daily snapshots. However, even with that being said in any hosting companies terms of service it is not their responsibility to make backups of your website. I would call it more of a courtesy service. No matter how much we love technology it is never perfect and it never will be. That is why it is important to be the Boy Scout and “Be Prepared.” I am guilty of the same sacrilege when it comes to not backing up my local computer let alone my website server and like most people it is due to time. Updraft – WP Backup/Restore helps eliminate some of that headache no matter what hosting company you are with. It runs a backup of your WordPress web content (uploads, themes, plugins) and WordPress database of all your entries and custom configurations. The really cool thing is you can backup to an Amazon S3 account if you have one, another offsite FTP account, emailed to you, or the traditional method of a directory within your webserver structure. *Note- The only downside to this plugin is that it currently doesn’t have an automatic scheduler for deleting older backups and with limitations on a shared hosting service you can reach your file size limit quickly. You can either FTP in and manually delete them or create a cron job to do that. Hopefully, the developers of this great plugin are working on something to make this a feature in the future.
http://langui.sh/updraft-wp-backup-restore

In any event, I run a lot of different websites using WordPress and no matter who the target audience is or what the format of the website these plugins are the ones that I find I use the most often. Don’t feel that you have to use these because it comes down to personal preference and I find myself mixing and matching as each website requires different functionality. The best thing you can do is try them out for yourself on a subdomain development version of your current or soon to be WordPress website so you can experiment and then later port your customizations to your live site. I hope this helps and as always, Happy Developing.

While Joomla had great backend 3rd party plugins like CRM, forums (VBulletin) and ecommerce bridge solutions like OS Commerce it was bloated and took a lot of time for a non-developer. Fast forward to today and WordPress has changed from a purely blogging focused platform to a more robust multi-dimensional website management tool without having an over abundance of programming knowledge.The great thing I love about WordPress now vs. then is that it has been easily adapted by programmers and plugin developers to be much more interactive and integrated with Social Media Networks for further exposure of marketing/advertising campaigns of a product or service.

WordPress works on both Windows and Linux based systems and is built off of php programming language, but has recently made strides in the jQuery (javascript), Java, Flash and Ajax programming languages. As an Account Manager for a web hosting company I would say we deal with more problems troubleshooting Windows based systems than our Linux based systems running the same set up using WordPress.

As far as e-commerce solutions there are a couple of pretty good choices without having to bridge an account like a forum. There is Shopp http://shopplugin.net/ and then there is one that our company is looking to offer with hosting packages called wp-ecommerce http://www.instinct.co.nz/e-commerce/. So in my opinion WordPress, in recent years, has gone from being just a blogging site and evolving into a fully interactive CMS website solution for businesses and Universities.Harvard is using a multi user version of WordPress called WordPress MU which is what wordpress.com runs on as well. http://mu.wordpress.org/

This summer I attended WordCampColumbus and some representatives from WordPress/Automattic http://automattic.com gave us glimpse into what they had in mind for the future including full HD video integration sans Youtube. http://videopress.com/ The great thing is because of the community support and the commitment of core developers from the company I only see WordPress gaining more market share. It use to be a lot harder to develop a website pre web 2.0. WordPress has narrowed that gap between traditional web developers and the average hobbyist. The best thing I like about WordPress is that it was named in the top three of CMS scripts that maximize Search Engine Optimization (SEO) out of the box. Drupal and Joomla were the other 2 in the top 3. I’m not going to provide a link on this because wherever you search you will get a biased review (including myself) so take it with a grain of salt. Just so you know, while I have talked WordPress up in my answer, I am in no way affiliated with WordPress, Automattic, or any of the other links mentioned in this answer. I just think it is a great php script that has really come a long way since its inception and will only continue to get better.