My buddy/colleague Randy Decker teaches Math 11/12 (British Columbia schools). He says:
"There's a free download of a Graphing Calculator on iTunes Apps Store. I'm quite impressed with it. I would recommend this application for use in Math 11 in British Columbia. It can tackle almost everything in the curriculum. Its display is far better than the Ti-83 or Ti-84. One can easily compare graphs because each is a different colour. It lacks a TVM solver. However, one can use graphs to solve some financial problems such as finding the time required to double an investment. One feature I really like is the ability to take a screenshot of a graph and email it."