Looks like I'm a bit late but anywayy.... We have just started using Mantis

I setup and installed Bugzilla but found it overly complicated particularly for noobs to use to report bugs.

So far it seems pretty good. It's pretty quiet on the development front, but it seems to work quite well. PHP + MySQL and it has been quite easy to add features I wanted.

I actually think I found it as a result of someone here pointing it out.