We've been using Bugzilla at work for a while now and it does it's job reasonably well. It works even better as an SSB (created with Fluid).

However, it does have a couple of small niggles - for some reason the columns in the search results are truncated, and you can only click the defect number to visit the defect. Luckily both of these can be fixed easily with some Userscripts: Click Row and Expand Columns.