Brunch at the Philadelphia Museum is not bad. The name of the restaurant is Granite Hill, its managed by Stephen Starr. Entrees run from 12-24 dollars, and brunch is served from 10:30-2:30. You can book through open table.
also walkable in the neighborhood is the diner little pete's, the bishops collar, london grille (never tried but i know they offer brunch, along with a bloody mary bar) and my personal favorite mccrossen's ($20 for a good meal and unlim bloody mary's and mimosas).