If anyone's in or plans to visit Baltimore, I really recommend the Clipper City tour. The owner (Hugh Sisson) conducted the tour we were on, and did a great job of explaining everything, in addition to trashing crappy beer. I've gone on two other brewery tours (Anchor in SF, CA and Dogfish Head in Milton, DE), and Clipper City's was very good.
The only thing I didn't like was that the tour is $5 (which includes 5 tickets for 1/2 pints and a glass you keep).
Plus we got blow-off splashed on us from a huge conical!