I'm interested in this as well actually, but I've never pulled the trigger. Well, to be fair, I did purchase a license for FogBugz a few years ago, but personally, I think it sucks and it's over-priced. I'm also specifically looking for something that's not SaaS (Software as a Service).

Commercial is fine, but it's got to be a more traditional software license where I buy and I install - without the FogBugz style limits on how many people can access the software. One of the crap aspects of FogBugz was that every account required you to pay more money - that means you couldn't realistically use it to let your community/customers access the site.

SysAID has a free version and I thought ZenDesk did too, but I can't find it right now.

So far, I'm most interested in RT (Request Tracker) which also happens to be free: http://www.bestpractical.com/rt/