Take the light rail:
http://www.mtamaryland.com/services/lightrail/
Both the Patapsco and North Linthicum have large (and free!) parking lots, it only costs $3.50 for a day pass, and there is a station just across the street from the Convention Center. The only minus is that the last train going south from the convention center goes by at about midnight, so you won't be able to attend any of the really late stuff unless you drive or take a cab.
I stayed around the airport last year (and doing so again this year) and it worked really well for me. It only takes about 10 or 15 mi