There is no denying that WordPress is one very popular PHP application, and that its popularity is well deserved, but perhaps what is more important is that WordPress provides a lot of flexibility in the form of plugins. WordPress Plugins extend WordPress by adding custom features (which may not be for everyone). In fact many of the WP Plugins do seem to be very specific, but there are a select few which have universal appeal. If you just installed WordPress, then your next task is to probably install all of these plugins or at least one of them.
WP-Cache 2 is my personal favorite plugin to install. I can’t honestly think why anyone would want to run WordPress without WP-Cache. As it’s name implies, WP-Cache does one thing, it caches your WordPress blog and immediately speeds it up. When first trying out WP, I was very disappointed with the loading times. It seemed to just pause. My MovableType blog never would take this long to come up, so it was definitely something I noticed about WP and other PHP/MySQL based applications that lacked caching. This is why I consider WP-Cache essential, because it adds a caching mechanism which is sorely needed in WordPress.
If you are using WordPress as your main site’s Content Management System, then you should consider installing these plugins too:
WP-ContactForm is the easiest way to add a contact page to your site. The hard way of course is to use a perl script like FormMail and verify that it is secure, or you can simply install this plugin and add your settings to WordPress and you are done.
WP-Shortstat brings web traffic stats to your WordPress Dashboard section. Most web hosts offer AWStats in cPanel, but how about if you just want something simpler and easier to acess? This is where the WP- Shortstat plugin really aims at, namely simple stats for your weblog.
Google Sitemap Generator is essential if you are interested in having your site indexed frequently by Google and if you want to help facilitate Google’s spiderbot by giving it a custom XML based sitemap to your site. The plugin gives you custom controls too, so you can add static pages from your site that exist outside of WordPress.
If you look around there are more WP Plugins, but most of them are either not as developed, or simply their niche is too unique for most general setups of WordPress.