Lived in "Charm City" (aka Baltimore) about 8 years ago.
Our absolute favorite place for crabs was Bo Brooks. Its about a 10 minute drive from the inner harbor, in the Canton area (and if you're venturing out to Canton, there are a good number of reasonably-priced pubs and smaller restaurants on O'Donnell Street. Be sure to check out Nacho Mama's if you're in this area)
If you can, avoid eating in the inner harbor pavillion area as most of those places are going to be quite pricey.
Also, be sure to check out Little Italy (only a few blocks East of the Inner Harbor) for fantastic restaurants and pastry shops. Our favorites were Sabatino's, Chipiarelli's, and Aldo's.