I grabbed a fish taco and enchilada at Maui Taco last night in C-3, and it wasn't bad. Not too heavy and reasonably priced (~$7 for a combo meal). Gallagher's also has some sandwiches and lighter items available from their surprisingly extensive menu. It's not like the real Gallagher's in the city, but it'll suffice for an airport steakhouse.

Au Bon Pain in C-1 and the food court near gate 74 (under the Presidents Club) has some decent light options. There's also a Vito's Deli, Ruby's Diner, and Le Petit Bistro in and around C-2 that are worth checking out as well.