there are numerous calcs for the itouch\iphone and they are all the same,
the one calc that i would love to see is one with new features like the Casio FX-991 ES, with Natural Display.
here's a picture of it:
-> 
and to make it perfect just to make sure it has the some past memory and
I you can see the last XX (whatever number) actions, just like Calc:
Thank you!
(if anyone takes notice)