There's some good places around...
Taqueria Del Sol is an all time favorite. I can eat at this place for days and never get sick of it. My favorite location is the one on Cheshire Bridge which is near Lenox Mall and Lindberg MARTA station. Taqueria's got its own bar but I'm underage so never ordered a drink there.
Another place to try is
Antico Pizza another favorite. I like the San Genarro. This place is BYOB so you can load up with whatever you want. Lots of people bring wine to eat with their pizza.
Oh, almost forgot about this place...
Hankook Taqueria. It's tacos with a Korean twist. Some have Korean BBQ or you can get bibimbap, lol. They also have some other stuff like sliders (I've never had it but people say they're good). DO NOT GET THE FIREDOG. It's not good at all. Personal favorite is the sesame fries and shrimp tacos. They're food is kind of greasy compared to the others but it's delicious.
The 3 places mentioned above aren't cheap but they aren't expensive either. I'd say Taqueria is about $10-18 a person and Antico is probably $15 per person. Hankook is probably $8-15 a person.
If you're willing to go on the expensive side,
Bones is great. Delicious food and great service. Looking at $50-80 a person and valet.
Are you looking for expensive, moderate, or cheap? I could recommend some good southern cookin' if you come to Marietta.