Here's a good one, or so it seems. I'm still deciding if I want to buy it, however. My TI-83+ I've had since 1997 took a blow to the screen somehow (I think -- hard to describe what's going on with it) so I'm looking for a replacement and might just get MathStudio for my Android phone. I don't expect students will ever be able to use smartphone calculators on tests due to the whole internet/cheating thing, but I mostly just use my TI-36X Pro scientific calculator on tests anyway.
MathStudio or TI-89 Titanium or TI-nSpire CX CAS or HP-50...decisions, decisions.