I'll third the mapquest, but keep your eyes peeled. I went to Otakon using MapQuest (from Albany, New York), had no problems in the slightest, but got a little turned around on the way back home... it could also be that I was driving at 2 in the morning on no sleep.
Future Cons: Otakon 2012 (?) Current Projects: OH, I HAVE THEM.
One piece of advice I will give is make sure to get return directions from mapquest or whatever rather than just trying to retrace your steps. Depending on where you are going, trying to get out of Baltimore can be slightly different then trying to get in. (It's all thoes stupid one way streets).