Other cloud storage tools for the iPad
We used to recommend Box, but its new CAPTCHA sign-in requirement does not really work on the iPad, making it impossible to log in if you forgot your password. Major fail.
Although Google Drive is supported by many apps natively, it's a good idea to also have the client app for direct access to your files.
Microsoft's OneDrive app is the default storage location for Office 365, Windows 8, Office for iPad, and Office Web Apps, so it's essential for Microsoft users. Few apps support OneDrive natively, so you'll need to transfer files.