A while back I briefly looked at the free version of QaTraq. Although I left the team I was considering it for before we every got very far with the project, it was the frontrunner of the options I looked at at the time.
It's got quite a nice interface, and what seemed to me to be a very sensible test planning structure. I think one of the big downsides was the the open source version didn't have table support in the WYSIWYG test case editor - Not a showstopper, and could be fixed with a little development effort or by spending some money on the professional version.
