Depending on what info (formulas, etc) there are on your spreadsheet you can try Numbers, QuickOffice, Office2HD, etc. the easiest way may be to type Excel into the App Store search engine.
As Gabriel has already stated, there are a number of apps that can be used on the iPad from viewing & editing Excel spreadsheets - I have Numbers, which is part of the Apple trio called iWork (Pages & Keynote are the other two) - this is a $10 purchase, but works quite well on the device; however, keep in mind that these iPad Excel simulators will not have the power & all of the features of Excel, so if your spreadsheets are 'complicated', problems may arise. Good luck in your selection(s).