I realize that FOSS is your primary desire and I definitely agree with this. If I were to limit myself to FOSS, I would go with RT 3.8, http://blog.bestpractical.com/2008/07/today-were-rele.html#screenshots
However, if you are willing to entertain commercial solutions and are looking for a Helpdesk-"ish" application. I just deployed WebHelpDesk with great success at my current employment, where I am the primary sysadmin and Corporate IT person. They just released a new version, 9.1.1 and it is very well done. The email integration is superb and beyond what I have seen with most other FOSS and commercial issue/bug trackers, given that it is built to run a Helpdesk and not be a software or source code issue tracker. It runs on Windows and *nix, they have a great demo and you can obtain a 30 day trial installer. I have become a big fan of this software and think it has a reasonable price of $250/year/technician (support person).
If you want more info on how we deployed it, please email me and I'd be happy to discuss it at length. I have no more connection with them than I am a very happy customer.