I went to Baltimore last fall and it was one of the most fun trips I've taken in a while. I really enjoyed the city and would love to go back!
Definitely go down to the Inner Harbor right along the water because there are tons of shops and places to visit there. The Aquarium is also there along with the Hard Rock Cafe, ESPN Zone (the food is really good and the atmosphere in there is perfect for sports fans), and other restaurants. We also ate at a really good place that had pizza and stuff like that but I'm drawing a blank on the name of the place. It was in the Harbor. If you have time I would try to do the tour of Camden Yards because you get to see the ballpark in a very different way and you also learn a lot about the history of the stadium and the Orioles (and it's only like $7). We did that when we were there and it was a lot of fun. Camden Yards is such a beautiful ballpark (I think Great American was modeled after it) and I hope you're able to take in a game there because it's a LOT of fun. They just got new HD screens for the ballpark too which look pretty cool, especially compared to the old ones I saw last year which looked like they were older than me, LOL