Downtown Atlanta rolls up the sidewalks at dark and everyone goes to mid-town or buckhead to party. So I dont know of any really great delivery services for the downtown area. I'm sure you can get the basics of pizza, etc, as there are two universities with dorms in the area (Georga Tech and Georgia State).
Not sure what you're looking to spend, but Buckhead Life Group includes several of the best restaurants in town and they have a really cool "card" program that works really well for incentive and appreciation type things and can be ordered online:
http://www.buckheadrestaurants.com