The TI-Nspire and TI-Nspire CAS are both slated to hit instructional dealers this Fall for educators (commercially available by Fall 2008), so we'd suggest pinching those pennies now in back-to-school anticipation.
The TI-Nspire lineup maintains the same relative form factor, but offers up a few swank advancements such as multiple representations, "grab-and-move" functionality, resizing, dynamic linking, and of course, the oh-so-sweet ability to save and edit in-progress work (shown after the jump) right on the device.