These days continuous integration (CI) becomes popular in software development 'cause it aims to support software developers to produce higher quality products. To apply CI in your project, usually, you need to use a CI server. There are many CI severs you can found: CruiseControl, Hudson, Luntbuild, Parabuild,... and most of them are free.
If you've ever heard about IntelliJ IDEA - the most intelligent Java IDE - is from JetBrains, you should know that they also have a CI server which has many innovative features, TeamCity. And today, JetBrains releases TeamCity 3.0, especially there is a free version.
For more information about TeamCity 3.0, you can find here: http://www.jetbrains.com/teamcity/
Try it out and have fun :-)