At my previous workplace we used TeamCity. It's very easy and powerful to use. It can be used for free with some restrictions. There is also a tutorial on Dime Casts. The reason we didn't use CruiseControl.NET is that we had a lot of small projects and it's quite painful to set each one up in CC.NET. I would highly recommend TeamCity. To summarize if you are toward open source then CC.NET is the grand daddy with slightly higher learning curve. If your budget allow you definitely go with TeamCity or check out the free version.
