The TI-89 (100x160 pixel display) is disallowed due to built-in Computer Algebra Systems.
The TI-92 Plus (1280x240 pixel display), which adds geometry & uses AA batteries instead of AAA, is disallowed for two reasons - because it also has built-in CAS and it has a QWERTY keyboard.
The TI-83 plus Silver Edition (64x96 pixel display) is really the next best option. "The TI-83 Plus Silver Edition is allowed for use on the PSAT, SAT I, SAT II Math IC & IIC, AP Chemistry, AP Physics, and AP Calculus exams."
Howver, it always depends on the intended use. I have a 10-year old doing pre-algebra and geometry - he's more interested in the games on them and I'm more interested in the ease of use. I'd rather get him into an HP RPN calc, but the whole class is centering on TI. So, am looking at the TI-73, 80, 82, 83 and 83-Plus Silver calcs. Will have to look at them locally first, then look for the best online deal.
You can get the 83-Plus (Black) for less, but the Silver's processor is "2.5 times faster, and it has over 1.5 MB of memory--10 times that of the TI-83 Plus". Also, it includes the TI-Graph Link to connect to the computer and download programs.