American- Clyde's (Tyson's, Reston, other places too)
American- Tuscarora Mill (Leesburg)
I like the Great American restaurants but sometimes they annoy me when everything on the menu comes with bland potato sides. But their flourless chocolate waffle is the best dessert anywhere, as long as they don't screw it up trying to put cranberries in it like they do (did? maybe it changed after the nasty letter I wrote them) at Coastal Flats.

Mexican- Rio Grande (Reston, Fairfax)
Tex-Mex- Chevy's
Asian- Pacific (Sterling)
Thai- Thai Luang (Herndon). This is an Idine restaurant. There is also some Thai place at the clocktower shopping center in Herndon that is good, but I can't remember the name of it now.
Italian- Avanti (Charles Town)
Pizza- Generous Georges (Alexandria) also Idine IIRC
Seafood- Joe's Crab Shack (Sterling), 220 Seafood (Winchester).