I have two wonderful tools that produce icons in tray. Last.fm allows me to hear music that is exactly my taste and TeamCity tray notifier monitors failed builds on TeamCity. However I wish that the icon for a failed build wouldn't be so much like the icon Last.fm produces:

Its failed build on the right and last.fm on the left. When they are both there its pretty obvious which is what because of the size. But when only the last.fm is there I constantly freak out for a short moment and think that someone on the Team broke the build and hasn't taken responsibility yet.

That being said, TeamCity is very recommended and is free of charge up to 20 users and 20 build configurations. Its a easy setup for building and running you unittests and on top of this it has a duplicate code finder. It integrates well with quite a few version control systems, we use it with Team Foundation Server and a check in triggers a build and test run on TeamCity.