Patapsco is definitely on the list of places to try. Dirt Rag had an article about I-70 last(?) month that included Patapsco. Rosaryville sounds good too! Thanks for the suggestions

As for Eastern MD: If you haven't been to Fair Hill Natural Resource Management Area, you really should! Oodles of well-maintained single-track, much of it unmarked. Ironically, the best map I've seen (and much of the trail maintenance there) are products of the Delaware Trail Spinners mtb club. http://www.trailspinners.org/2008RaceMap.pdf. The "official" map is ok, but not great.