We're using Bitnami's Redmine Stack (a single-installer for the whole Redmine package, including Apache), along with the nascent Redmine/Mylyn server-side plugin and Eclipse.
It's too early to tell how well this all really works, but Redmine has so many other useful features (such as a Redmine TortoiseSVN plugin), we're bound to use it. If Mylyn works as well, that's a bonus. Obviously we're new to Mylyn and not dependent on it, although it looks extremely useful.
In my opinion, Redmine is much more functional than the other systems mentioned here. I do not have extensive experience with them, however, so take that with a grain of salt. It absolutely warrants a close look.