Joe Leary on his blog says:

As part of the State Portal project we need a bug tracking system. A quick search of the internet provided a reference to a free bug tracking package that seems simple to install and use.

I'd recommend Bugzilla.  My experience in this area is that you want a very good bug tracking system that will scale well.  Since we'll want to expand the use of any successful project to other areas and projects, we should use something that can go the distance.  Bugzilla will do that.