Hey Chickmagnet, (Nice name!) The Best place to go for 18 and up party in Atlanta is Wild Bill's on Wednesday nights. This is their College Night and it is...well, WILD! DJ Mike B spins everything from house, to hits, to hip-hop! There is usually 2000-3000 people out for this!
Also Moe's and Joe's in the Virginia Highlands has a good 18+ party.
The Masquerade has lot's of Live shows, most are all ages. That is really the only all ages venue, (your 17 year old friend may have some challenges trying to get in to most clubs here.)

The most high end clubs in Atlanta are: Eleven50, Tongue and Groove, Cosmo/Lava, Halo, Vision, Compound, Club 112, The Mark, Sutra Lounge and Wild Bill's. Coyote Ugly is not a Dance Club but still a really good time!

I hope this helps! Have a great time up here!