At BWI it is the Ramada. I think for around $60 you get a room for the night, free parking for the week and free shuttle to the airport. Maybe even breakfst too. They run ads in the Baltimore Sun just about every week.
I park at FastPark and have been happy with the service. I think it is $9.75 per day and they have a frequent parker program. They always send me $2 off coupons. I have a lot of them.