For hosting common files it's ok. Also it is on Android too do, great to transfer files between your Windows and your phone. But if you want better security you have to subscribe a monthly offer.
CalPrint - CalPrint uses your existing reminders and calendar entries on your iPad or iPhone (Exchange, iCal and Google Calendars etc.
Dropbox - Online Sync and File Sharing
Air Sharing - Air Sharing lets you bring your documents with you — without bringing your computer.
Google Drive - Access and sync your files anywhere
Print - Developers of application solutions for the iPad & iPhone. 'Printing on the iPhone: “There's an App for that” - Print & Share' as featured in Apple's “Office” iPhone commercial
Mega - Secure File Storage and collaboration