The bikewashington site is one of the best resources for DC trails.
The trail along the Virginia side of the river is the Mount Vernon Trail. 19 mile length. Very pretty ride and VERY popular. Gets crowded on weekends, but weekdays should be ok.
Connects to several other major trails:
-Memorial bridge gets you to the Mall, Hains Point and other spots along the River Trail.
-Key Bridge takes you to the C&O, Capital Crescent and Rock Creek Trails. The "zoo review" is a good loop on weekends, and the C&O to Great Falls is a good ride.
-The Custis Trail and the Four Mile Run Trails get you to the W&OD, 45 miles long from Alexandria to Purcelville. The western part near Leesburg and Purcelville might be nice if you're on a longer visit.
Last edited by cc_rider; 04-19-06 at 04:57 PM.