Those casio ones are good, I have the FX-83ES, but the graphical calculator which my friend has frankly does the questions for him. Draws the graph, points of intersection etc.
I know you can do a lot on the FX-83ES but not quite to the standard of those graphical calculators. I forget what model his is, but it cost him about 40 quid through his school. I thought it was cheating the first time I saw it.
I think having one earlier would have made me extremely lazy though so I am kind of glad I just have the 'standard' casio FX-83ES.
EDIT: I think he uses the CFX9850GC+