When people ask me why I run my web server on linux, the main reason is Apache, and when they ask why I like Apache - the modules. I mentioned yesterday that mod_rewrite is one of my favorite apache modules, here is my Top 10 Apache Modules list:

1. mod_rewrite - Allows you to match url patterns with regular expressions, and do a transparent redirect, or apply a HTTP status code response.
2. mod_deflate - allows you to compress content before sending it to the browser using gzip compression. Browsers have supported the ability to automatically decompress the content for you. It saves lots of bandwidth (sometimes up to 70%), and decreases page download times.
3. mod_security - a module that lets you block content based on form post data, urls, pretty much anything in the request.
4. mod_speling - this module performs spell checking on a url. If your moving from windows to unix (case sensitive) this can save you a lot of time fixing case problems.
5. mod_cache - a content cache keyed to URIs. You can cache in memory, or to disk.
6. mod_setenvif - allows you to handle different environment variables, can be used to block email harvesters, referer spam, etc.
7. mod_auth* - You can authenticate against pretty much any repository you can think of with one of the mod_auth modules, eg mod_auth_mysql, mod_auth_ldap
8. mod_ssl - HTTPS support for Apache.
9. mod_proxy - Turns Apache in to a Forward or Reverse proxy server.
10. mod_benchmark - stores benchmark info and provides charts.

What are your favorite apache modules?