Bars are everywhere, but you'll find concentrations of bars in Buckhead, lounges in Midtown, and bars Downtown.
Some worth mentioning:
[*]Buckhead - Twist (tapas bar). Tongue and Groove
[*]Midtown - Bazaar Urban Bar (lounge), Halo Lounge
[*]Downtown - Trader Vics (Polynesian-themed bar). The Mark
For clubs, you *must* head into Midtown. Where you go depends on the music you like and whether you go to dance or simply be seen:
Oh, and to get loopy for just $5, enjoy the tasty, "free" beer at Atlanta Brewing Company
every Friday at 5PM, then stumble over to Rocky Mountain Pizza. Both are hits with the students at Georgia Tech.