On the iPhone, Mariner Calc gives you the ability to view and edit native Excel files (Excel 97 and up). You can also wirelessly transfer to and from your computer.
Mariner Calc also has support for 32,000-by-256 columns, multiple sheets and many functions including 24 math functions, 18 finance functions, 17 trig functions, 13 statistics functions,
14 lookup functions plus logic, date, text and info functions.
Mariner Calc is available for $9.99 from the App Store.