From my experiences - here are my recommendations:
Atlanta -
The Renaissance Hotel is hands-down the best location for spotting in the U.S. You are literally surrounded by the action, and you are maybe 500' from the runways. All the rooms have balconies, and if you get up high you have a view that is simply spectacular. They even have spotter rates and packages on weekends!
This photo shows you just how close to the action you can get:
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Photo © Mark Beckwith
The Sheraton Gateway is also a good spot, but it's nowhere near as good as the Renaissance. You can get departing or arriving traffic fairly well from the lounge on the 12th floor (although the tinted windows can present a challenge if the weather isn't perfect).
Dallas -
The Harvey Hotel has a pool deck, and is pretty good for spotting, although you're pretty limited on what kind of traffic you'll see. You are at the southeast corner of the field, which makes spotting the heavies a bit difficult, but you have a great perspective of the runways. Approaching traffic is blocked by the gym, you really can't see the approaching aircraft until they are right on top of you - but at that point they're maybe a couple hundred feet over your head. It's a cool view, and well worth it. I captured this image last year from up there -
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Photo © Freight-Dawg - Airside Photography
Enjoy!
Drew
[Edited 2006-01-17 23:22:28]