I have gotta 3rd the RT suggestion. It can be heavy or lite.. I ran it on a laptop with Pgsql for a client for months accumulating thousands of tickets without a hiccup.. it's Perl using Mason..

However RT is not explicitly tailored to software bug tracking per-se, as it would be devoid of many "fields" or "categories" one might consider de rigeur for the application, such as contained a typical looking bugzilla ..