iPad has spreadsheet options that will open and display Excel files, but probably not with perfect compatibility. I know it won't handle some of my Excel spreadsheets.

Microsoft just came out with the Surface tablet which will run Excel. I haven't heard too much whether it is a crippled version or not, but I do know it won't run macros (as one example of a limitation).

I'm waiting for the Surface Pro to come out. That version will run a full version of Windows which will run normal desktop programs. I'm interested whether it will allow all Excel features to work.