I'm a CruiseControl.NET user all the way. My teams uses it at work and I use it at home for personal projects.
In particular, CruiseControl.NET allows me to run through the whole CI process: builds, version update, unit and integration tests, archival of source or release candidate, code coverage, even deployment to our test system at work. It's highly customizable, works well with MSBuild and NAnt, and even had an extensible plug-in architecture.
It pretty much does everything I need.
The biggest disadvantage: configuration is sometimes a pain, and can take time. But once it's done, it's done, and as another poster said, I love seeing the "successful build" signal because I know that not only did the build itself work, but that also that my unit and integration tests all ran successfully.