apps

Popular apps that support those document types are Apple's Pages app for Word documents, Numbers for Excel spreadsheets and Keynote for Powerpoint. And from third-parties apps such as Documents To Go ('premium' version) and QuickOffice Pro HD.

Have a look at the following:

http://itunes.apple.com/sg/app/quickoffice-pro-hd-edit-office/id376212724?mt=8&l s=1

http://itunes.apple.com/sg/app/office2-hd/id364361728?mt=8&ls=1

http://itunes.apple.com/sg/app/documents-to-go-premium-office/id317107309?mt=8&l s=1

http://itunes.apple.com/sg/app/polaris-office/id513188658?mt=8&ls=1

There are MS Office compatible apps available in the app store like Quick Office Pro and Documents to Go. Apple also has their iWorks suite of apps, Pages, Numbers and Keynote that are compatible with the MS Office apps.