The W Midtown has Whiskey Park which Is a club/lounge and I believe The W Buckhead and W Downtown has something similiar (check all of the W Hotels in Atlanta here
www.Whotels.com/Atlanta).
The Glenn Hotel Downtown has a nice rooftop lounge and they often have parties there with dancing
http://www.glennhotel.com/.
Twelve Atlantic Station (In Midtown)
http://www.twelvehotels.com/Atlantic...n/HotelHome.do often have promoters who rent their lounges out for parties usually around the 1st of the month

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All these Hotel clubs/lounges target a 21-40 demographic... Hope that helps!