I’ve been a big fan of test-driven development (and unit testing) since I first learned about it a few years ago. It wasn’t until this month that I learned about NDbUnit. This little library is a great value-add for unit tests that involve databases. The creation of test data is tedious if done manually (NDbUnit uses XML for data files), but that’s the only real drawback I’ve found so far in my limited experience with it.  It plays very nicely with NUnit, MbUnit, and TestDriven.NET.
You can get binaries and source code for NDbUnit from Quality Labs.  I also put together a (very) small sample project with Visual Studio 2005 that you can try out.