Just before my job changed last year, I had embarked on a modernization of some the technology I used in my 8th grade algebra class. In particular, I sold off all the TI-83 graphing calculators and used the money (plus a little more) to buy a class set of iPod Touches. I had a plan to install several very useful tools on these iPods, but my favorite one was the Graphing Calculator App:
I loved this app because of its colorful, dynamic presentation of graphing. It allows easy zooming and moving around the screen. The TI-83's were an old technology and overly complicated to use. The iPod touches were simple, expandable and downright cool.
I recommend this app to any and all teachers of algebra.