I don't like bugzilla that much, my favorite system is RT: Request Tracker.

Free, uses perl/mason and mysql, and I found it intuitive to work with and relatively easy to customize. i.e. although I'm not a perl guy, I added RSS feeds and such to my installation. The only problem is that the developer keeps coming up with new versions. Finally got 2.x where I like it and he's already made the first 3.x release. And yes, the database format does change between major releases, sigh.