TestMatrix by ExactMagic
I've been using a tool called TestMatrix, which has a lot of features that Test-Driven Developers will love. This tool features a test explorer that contains a tree view listing of all the unit tests in a unit test project. Simply select one of the projects in the drop down, and all the unit tests load in the sidebar. You don't need to run all the tests in the sidebar; it is possible to filter out the tests to run tests by project, namespace, single file, or specific method. The last two can be performed by a right-click menu option in the test explorer, or my personal favorite, in the unit test itself.
So, say you just created a test and finished the code. By right-clicking at the test level, you can run just a single test. By clicking anywhere else, you can run the whole unit test. When you do, everything runs in the background on threads (which works really well; I'm on a 512 MB machine and it works pretty nice) and the tests run right in visual studio itself. No need to run the project or open it up in NUnit.
Upon running the test, it loads the results of the test in test explorer, and a test results window at the bottom of the screen. But, even better, the results appear in the left pane (the gray bar next to the left of the line numbers) which tells you performance information (sec/ms), code coverage (a little red bar that states which code was not hit), and some other information.
This is a very beneficial tool that makes running unit tests very convenient. I really love working with it, and I'd thought I would mention it to others.