We've been using JitBit for about 6 months now and I'm pretty happy with it. It isn't very feature-rich but it keeps track of tickets just fine. There are probably equally good free solutions out there but now that we've paid up we might as well stick with it.
Quite a while ago I configured our old phone server as a monitoring box running Nagios and Cacti. The combination has been invaluable to me. There is nothing more satisfying than getting a call from a user about a problem and being able to say that you've already found and fixed it. The configuration requires a lot of manual work but it was definitely worth it.