We've been running our IT Department without a helpdesk software package for way too long. Initially, we only had one full time support person so it was pretty easy to just use email to track stuff. Over time we've grown an distributed some responsibilities so it was time to get a decent package put in so nobody dropped the ball on anything. I took a look at HelpStar, Cerberus, OSTicket, OTRS and SupportSuite. Each has an interesting take on how it handles tickets, but I ended up going with SupportSuite. My reasons were based on price; features we'd actually use, something that runs on Linux (CentOS), email ticket submission, visibility on a PDA (some type of decent web interface), unlimited users and techs (without having to pay ransom per tech) and ease of use.
We are still in the configuration stage, but all looks good so far. I really like the LiveSupport piece which is kind of an IM client for the techs that are on-line. I also like the escalation, SLA, and Teamwork features. All this for under $700. Some of the solutions I looked at were almost $1000/tech. That's just way too much spend on something like this. Heck, if all goes well the users won't even see it. Hard to justify something at $1000 per tech when there's little direct visibility for the users.
I'll let you know how it goes but so far so good.