Javaworld has published a comparative review of four open source continuous integration tools:

Conclusion:

Many CI tools are available out there, and there is no one-size-fits-all solution. Different tools will suit different environments and different people. At the end of the day, to choose the right tool for you, you need to set up the tools and try them for yourself. Hopefully I have given you some tips to help you investigate further.

As stated in the comments of the post, if you want a complete list of CI sytems, you could check the Continuous Integration Server Feature Matrix.

(Via Artima Developer)