TestRunner for NUnit
I installed TestRunner for NUnit because I've never been wild about the existing NUnit add-ins available--it just feels only half integrated and when things start to get flaky in the IDE the clunkiest add-in is going to be the first thing I disable or remove. In these scenarios I'm biased against software that's only half put together. In any event, I tend to just use the NUnit standalone GUI or console on another monitor.
One thing that would be nice is the ability to debug seamlessly in VS .NET, but launching the NUnit GUI and stepping through that way works pretty well. TestRunner takes a slightly different approach and attaches to your existing VS .NET instance and then lets you debug. There's a little cruft in there though because you have to select the debugger each time and it therefore has a higher transaction cost to me than launching the NUnit GUI with your fixture.
It's really six to one-half dozen at that point, but it makes me want the even more seamless approach where I just build, run, step, nothing else. This is only particularly useful during those stretches where I've broken a test or am trying to nail a fixture down the first cut through. For whatever reason, even after a couple years of this, I haven't yet gotten to the point where I find diagnostics through the unit test harness are as efficient as conventional stepping/watches/asserts through the IDE. Everything I read tells me I may one day forget what a debugger is, although today that seems like a distant milestone. Ugh, I just used 'milestone' conversationally.
Anyway, if you run the NUnit VS .NET add-in or are interested, give TestRunner a shot. I prefer it so far, it seems a little more smooth at doing quick runs inside the IDE and has some additional functionality. It does lack some of the exception, Console.Error, Console.Out stuff that I like about the NUnit GUI.
No source though and it's bound against NUnit 2.1.4, does not like 2.2 yet. Those would be dealbreakers for a lot of people, I haven't tried machine.config rewiring though. There's also a Whidbey-compatible version which is a nice bonus.