The following WordPress plugins have been tested to work on our servers; and can improve your WordPress designed site / blog:

AddThis featuring Sharing Buttons/Facebook Like/Tweet Button
This plugin allows you to easily set up buttons at the end of each post, page, etc. (this is all easy to configure) where the reader can share the content with friends, family, and co-workers via Facebook, Twitter and so on making your content more viral (which can be a good thing).

Better Delete Revision

WordPress keeps revisions of pages and posts that you update which over time consume more and more disk space, and can impact the performance of your site. Install this plugin, and use it (it will be in the settings area) on a regular basis to check for revisions to delete to keep your WordPress database optimized. There’s also a section to optimize the entire database (I recommend using that after deleting revisions).

Broken Link Checker
If you are like me, you will have links to external sites (or even within your own site). This is a great tool to check and report broken links as well as redirects you may not remember. This tool also allows you to fix the links from within its interface rather than forcing you to edit the page or post.

Collapsing Links
I’m told one’s WordPress pages load faster the less that is immediately displayed. If you have areas such as a blog rull or useful links, conserve space on the page or post by using collapsing links. Visitors can expand and contract the links as they see fit.

Fast Secure Contact Form
While I’m told Gravity Forms is the cream of the crop for WordPress developers and designers, I’ve found for day to day easy use, Fast Secure Contact Form does the job. Please note: make sure the wp-content/plugins/si-contact-form/attachments is chmod 777 for permissions using your FTP application.

Google Analytics for WordPress
This plugin makes integration with Google Analytics a breeze.

Google XML Sitemaps
This plugin helps with your search engine rankings. In order for it to work on our hosting, just after plugin installation and activation, but prior to creating the first site map, using your FTP client, create two empty files:

Then change their permissions to chmod 777, which allows the plugin to update the file.

Hyper Cache
This plugin can help your site perform faster by caching content. Please make sure the wp-content/advanced-cache.php file is set to 777 via your FTP program permissions, chmod; and, make sure the wp-content/plugins/hyper-cache/cache directory is set to 777 for permissions (chmod).

Login Lock
When you are on the Internet, you should be of the mindset that hackers are out to get into your personal computer as well as your site (it is not a matter of importance/signficance as much as it is a matter of stealing computer resources). Login Lock allows you to better protect your WordPress admin area.

No Self Pings
Pings from other web sites can be a good thing, but if you do a lot of self linking within your posts and pages, it can be an administrative pain to delete those self pings. This plugin takes care of that for you.

Permalink Finder
This is a very neat plugin that will automatically try to redirect a visitor to the appropriate page if you’ve updated your Permalinks and forgot to update all of the links for the changes.

WP to Twitter
This is a plugin which allows any new posts, pages, or updates to posts and pages to be sent as tweets using your twitter account.

Yet Another Related Posts Plugin
This is a neat plugin which allows you to set up conditions for what is to be considered a related post. Then on a post, you can display those posts which are related to help guide a reader along on your site or blog.