IIRF or Ionic Isapi is a small, cheap, easy to use, URL rewriting ISAPI filter that combines a good price (free!) with good features. It is reasonably fast, and reasonably powerful.
But for Joomla! users who want to use SEF, it can be a pain in the ass.
I figured out how to use it with Joomla! and with 90% of the top rated components.
You can use my file for free.