Buying a US (micro-) SIM on arrival in Dulles?

Hi,

I can't seem to find much information about it, but is there a place to buy a SIM for my phone in Dulles? I will be in VA for 2 weeks and will almost exclusively use data (and Skype), though don't really need all that much data (500MB would be more than enough).

Another option is to try to order from Amazon or a phone company directly and have it shipped to my hotel, but am not sure who to choose.

Thanks

Dr. PITUK