I would highly recommend taking some classes at Wired Cycling in NE (www.wiredcycling.com). Look for Leti, Claudette or Lauren (me) on the schedule — all are serious cyclists and/or triathletes and teach accordingly — but all of the instructors are great! They’re all equipped with power meters and cadence sensors, so you can track your progress and ride accordingly.
Off Road is also an awesome studio with a lot of cyclists and triathletes on the schedule. A couple of NOVA bike shops also offer Computrainer classes (The Bike Lane Reston and Green Lizard Cycling). Another favorite instructor who is into cycling is Dru Ryan — he teaches at Mint, Biker Barre and Equinox.