With everything pointing towards them losing the iPhone exclusive, they may actually try and put out some decent android phones now. Or you could get a unlocked Desire HD from Canada that will be releasing soon.
Rumor mill is that Motorolla will drop a flagship, high-end device for ATT soon. Check out the "rumor" forum below this one.
On the other hand, Captivate and Streak are the only real choices for Android (oh, and the Aria).
It seems as if ATT wants to focus on Microsoft and WP7 as they are releasing several more WP7 phones. So, I think that is the direction they are taking ... staying away from the open-platform and looking at the two big locked-down players (Apple and MS). Which is fitting for ATT, the carrier who likes to lock-down services.
I think Android will be only a few top-shelf devices.
Rumor goes AT&T might get another HTC Android. Code name Paradise. Appears to be a slider. That alone implies it maybe AT&T's version of the HTC Vision (G2, Desire Z, Merge, Shift Evo).