Just wanted to let everyone know PocketCAS is on sale at the moment, for $2.99 from $9.99.
I am not the developer. I bought it a few months back and have enjoyed using it. The CAS engine is based on XCAS, and it provides some other nice features.
Edit: added link to PocketCAS homepage.
Edited: 25 June 2013, 6:40 p.m.