I love RT. Real solid product with great hackers behind it. And you did not mention that it is open source and takes hardly 1-2 hours if you know your way through CPAN and Apache.

The latest 3.8 is not that bad with new theme.

I can even do a free install/setup for any non-profit.

http://bestpractical.com/rt/

And don't forget the http://hiveminder.com/ from same company.

EDIT: Added links.