The venerable Backstreet is long gone. Here's an overview of gay bars in Atlanta:
Blake's on the Park: Nice neighborhood bar with lots of drag shows. Always busy, including Saturday and Sunday afternoons. DJ but no dancing. Usually a younger crowd.
Mary's: Fun, funky place in East Atlanta. One of my favorites. The crowd is a mix, the bar is really narrow so it fills up quickly. Two nights a week they have Maryoke, otherwise there is a DJ, and some dancing usually breaks out though there is no real dance floor. Mary's often has oddball theme parties like Bastille Day or Hanky Code. There's also an upstairs lounge.
Eagle: Leather bar with a DJ and dance floor. Very bearish, slightly older crowd. Also a huge deck on the back for when the weather is nice.
Woofs: Atlanta's gay sports bar. Bearish crowd. Serves bar food and it's pretty good. Lots of TVs for watching games. Also pool and darts.
Heretic: There are fewer and fewer dance floors in gay ATL, but the Heretic has stuck around. Darkly lit bar with several rooms and a deck. The central room is a dance floor with a DJ. A lot of shirtless dancing here. The crowd used to be pretty hot but WetBar took a lot of the pretty boys away. Now that WetBar is closed, we'll see.
Jungle: First it was Jungle, then a country bar (Wild Mustang), and now it's Jungle again. Large nightclub with large dancefloor and a DJ, pretty busy when it was the old Jungle, and was still busy as Wild Mustang. The old Jungle crowd will probably go back.
3 Legged Cowboy/Hoedown's: Atlanta's gay country bar. Almost always busy on weekends. Friendly crowd and staff. DJ/dancefloor, lots of country dancing.
Burkhart's: A neighborhood bar. Also serves bar food. Lots of drag. Used to have a gospel drag show on Sundays that was very popular, but it's long gone. Now it's the Armorettes on Sundays, which still draws a crowd. Check them out if you like camp drag.
Amsterdam: A nightclub divided into two sections: a darkly lit dance floor area with DJ and a brighter bar with TVs and music. A hot place when it opened a few years ago, but the crowd has fallen off a lot. So it's hit or miss.
Bulldogs: a bar that serves mainly an African-American crowd. I don't know much about it.
My Sister's Room: Lesbian bar. Haven't been so don't know what it's like.
Opera: a new club, haven't been.
Swinging Richards: An all-male, all-nude strip club. Yes, they take it all off. No, you can't touch (wink wink). The cover, the drinks, and the dancers are expensive. But I usually manage to have a good time anyway :) This is not a gay bar; there are lots of straight women customers too.
Those are the major players. There are lots of other smaller bars that I don't frequent or are outside the city.
Dress Code: Most of gay ATL is a Jeans & T-shirt crowd. All the places I've listed above are casual dress or more if you want.
Very circuity crowd. Hottest guys dancing in town. Cut circuit boys, daddy muscle bears, take your pick. Most die-hard partiers start either at Blu or Heretic at midnight/1am and then move to Backstreet at 4-6am and dance till daylight. Saturdays and or special holidays and events are the only decent times to go.
Dress Code: Wear a shirt that you can take off and tuck in your pants/shorts. It's expected. And yes..it's hot enough in this town during the summer that many locals wear shorts out to the clubs.