FogBugz
I have spent some time this week reviewing and testing FogBugz as a PM tool for us.
http://www.fogcreek.com/FogBugz/
We have a home grown FoxPro app that we use that does an OK job. I have been looking for something inexpensive that was built specifically for PM though. So far I like what I see. APress sent me a free copy of Gunderloy's "Painless Project Management with FogBugz".
http://www.apress.com/book/bookDisplay.html?bID=436
I recommend this book if you do plan to use FogBugz.
I will report back with more over the next week or two.