I have been creating more and more sites with WordPress. I have found it is a great tool and easy to configure. Since I enjoy working with PHP, WordPress makes customization easy. One of the many features that allow WordPress to be a very robust tool is the ability to use plug-ins.
A plugin I recommend to everyone is a caching plugin. Caching is a great feature to speed up your site. For those not failure with caching it allow for files on the web server to be stored statically and delivered faster to the browser. Read more on WikiPedia (caching)
In WordPress there are a lot of options for caching. Here is a great article describing a comparison of some of the top caching plugins. (The best caching plugin)
I tend to agree with the author on the W3 Total cache (http://wordpress.org/extend/plugins/w3-total-cache) as one of the best, but on most of my wordpress installs I stick with WP Super Cache (http://wordpress.org/extend/plugins/wp-super-cache)
Super Cache allows you to have a view of what is in the cache and also tweak some general settings. It is not as robust as W3cache but it allows me to quickly and safely create cache on a site.