Make sure you register with ORBITZ before you start looking for flights. I was registered and when I found a flight, it told me I had to reregister. By the time I got back to the search screen, it told me my flight was no longer available!
Also, USAir now has really cheap shuttles between NYC, Boston, and DC. I don't know if that helps anyone out. You just need to fly between certain weekdays or if you fly on the weekend, it needs to be a Saturday departure. It's under "Go Shuttles."
Also, if you're on the east coast, look into AirTran. Although, they used to be ValuJet, so I'm a little wary of using them!
Good luck.