DC and the surrounding area are great places to ride bikes. Pick up a copy of the ADC Bike Map for the DC region. Check out Potomac Pedalers (bikepptc.org) and Oxen Hill Bike Club (ohbike.org). They have in-town rides, mountain bike rides, and road rides farther afield.

Not much snow, though. If that's really important to you, I doubt you'll stay long. Kayaking is great, however.