Sam Grow is pretty big and local (when he's in town). Plus he's got original music instead of a bunch of covers.
Ryan Forrester Band here in Calvert is pretty good. I'm sure they have original music, but most of the time they do covers because that's what most people want at their local bar.
No Green Jelly Beenz
Ballyhoo (though not a SoMD band, they are a MD band and occasionally come to SoMD)
One Louder does a lot of 80's cover music (if they are still together).
I know there's a bunch more out there, but those are off the top of my head.