If you're not married to trout, the upper, free flowing parts of the
Patapsco River have received high praise for bass and trout depending
on where you are. I'm not as familiar with it, but my best fishing
buddy swears by it, as does Frank R. here. Frank has also fished the
Little Patuxent. (Hell, Frank has fished damned near every body of
water in the area; why he moved to Nebraska is beyond me. g)

I'll have you know that there are huge brown trout in the Missouri
River. Unfortunately, they are about 1000 miles upstream. Oh well.
I'll second the comments about MD waters. Go to the fly shop in Bass
Pro and get the book from Larry Coburn (he runs the fly shop) on
Maryland trout. There is a piece on each river that has a naturally
reproducing population. A great book for anyone wanting to fish in
Maryland.
4 wt rods with black wooley buggers make for some real fun fishing on
the Patapsco. The smallies are up to 2lbs and they are a blast.
Enjoy.
Frank Reid