I live near Baltimore, too, so you could come visit me, lol
I would also recommend the Aquarium. It's really good, Maddie LOVES it....
The Zoo is ok, but I would say don't do it.... we have a membership, but it's not nearly what it was when I was younger (not as many animals and things)... plus it will be hot, so that wouldn't be fun
And I am just pretty forgetful, what does your DH do??