I have been using TestDriven.net as a tool now for a few weeks, and I have to say that it is a fine addition to my tools collection. It gives me the flexibility I need to run tests in any manner I choose, simply by right-clicking. It's a Visual Studio add-in for 2005, and 2008, and it works seamlessly with a variety of test frameworks (NUnit, MbUnit, and MSTest being the most notable).

Speaking of NUnit, another excellent tool that I find invaluable to help me test my code. NUnit now has RowTest extensions (like MbUnit) in the production release (2.4.7 and if you aren't using this version, you should upgrade), and Parameterized Tests coming soon, and they look really cool. I find that I can replace a lot of repetition in my tests with this row based system. It enables me to write more tests faster, and that's always good. I am hoping that the new release goes into production mode very soon.

UI testing with Selenium is another favorite topic, I will write up another article later with examples of how to do real automated user interface testing using NUnit and Selenium. However, feel free to start playing with it now... its a great tool also, and plays nicely with the other tools in the toolbox.

Use these tools in good health, to help get your code into production as bug-free as possible by testing the heck out of it!

P.S.
Please make your unit tests into separate assemblies... no one-massive-monolithic-test assemblies please... and the tests should run FAST. If you mock out all the database, network, web service, etc. calls, you should be able to get all of your tests in an assembly run in under 5 seconds. Aim for a target of 100 tests per second, and you will be a much happier camper.

If you are a real stickler for this (and I recommend it...) add this code to your test assemblies:

private static DateTime assemblyStart;

 [ClassInitialize]
 public static void MyClassInitialize(TestContext testContext)
 {
     assemblyStart = DateTime.Now;
 }

 [TestCleanup]
 public static void TestCleanup()
 {
     Assert.IsTrue(
         assemblyStart.AddMilliseconds(5000) > DateTime.Now,
         "Tests took too long to execute.");
 }

Enjoy!