We use TeamCity, from JetBrains. They also make Resharper And IntelliJ.
We use it for building our .Net applications, and it has been quite easy to set up, connect to TFS, and run additional tools from. It is very polished, and actually kinda reminds me of this site. Found it much nicer than CruiseControl, and for our team size it is free. If you need lots of different builds, more per-user builds, and so on then it costs a bit (but still quite reasonable).
