From the ImproveSpeed.info blog there's a recent post about a quick way you can speed up your WordPress site (especially one that gets a higher load) by making some modifications to your .htaccess file.

It is known the importance of the page loading speed over the traffic of your blog. Recently there were a lot of discussions and probably the page loading speed will become an important SEO factor for google and other search engines. The main problem with the existing .htaccess file is that the RewriteCond directives checks the existence of a file on disk when it is not really required. Each access to disk increase the page loading time.

They show how to take the stock .htaccess configuration and modify it (still using mod_rewrite rules) to get a bit more fine-grained in the filtering of how requests are handled, things like having the index.php requests are forwarded automatically on or not caring about images or CSS.