MCTS: Active Directory 2008, Configuring
That's it, and it's completely unrelated to my job. I run Linux :). Why did I get it then? It was free from MS, required less than 6 hours of studying, and my boss paid me and my co-worker to go take the test.
I'm of the opinion that most certifications that aren't lab based aren't worth it. The only time it may be worth your time is for consulting or for an HR screen pass.
My current employer doesn't even like paying for certifications. They'll put you through all of the required training up until the point where you could get your cert (i.e. they care about the knowledge), but they won't pay for the actual certification unless you have a pretty good reason for doing so.