Man I miss biking in DC. I moved to NYC in 98 so maybe some of this is old data:

Northern VA is heaven if you like paved trails. Get a bike path map and a good map of the area and go out. A really great ride is to take Rock Creek down from Maryland, through the City, through the Zoo to Georgetown, Cross the Key Bridge and pick up the path that goes along with the GW parkway. You can ride this the whole way down to Mount Vernon. Makes for a long ride (maybe ~30-305 miles one way) but it is very peaceful and there are some nice nature spots down past Alexandria. There are a lot of paths on converted rail beds all around the Arlington/Alexandria area.

Great bike/veggie food can be found at Teaism... in Dupont off Connecticut.
Juilio's pizza on (from memory, sorry) maybe 16th and S(??) is great in nice weather. Great pies and a nice rooftop deck.