There is a "lounge" thing near the Southwest concourse (C I think?). You take an elevator up and it is like a small aviation museum. Theres some chairs overlooking one of the terminals and some taxiways. Closest thing to a lounge BWI has. You'll see me there (delayed) on friday afternoon... White/orange sailcloth bag, come say hi...

Edit: It is called the "Observation Gallery," between B and C. It is located in a hall sort of behind the ticket counters but not yet through security. It's usually very quiet up there.