Zoho, a collection of Web-based office tools, has recently rolled out an iPhone-friendly suite of applications. Called iZoho, it provides access to Zoho Writer, Zoho Sheet, and Zoho Show. The iPhone also supports Word docs and Excel spreadsheets, but the iZoho application lets you edit certain documents like the Zoho Notebook.
iPhone link: http://mini.zoho.com/
Web site link: http://www.zoho.com