With Fileboard you have all your documents on iPad

Fileboard is simple and free application for iPad through which you can see all documents and files you have in Gmail, Drobox, Box or Evernote. Fileboard is a service created by the co-founder of Inbox2, Khuram Hussein.

In addition you will have access to your files from various services, what's great about  Fileboard it is that you can use it as email client.

The login service syncs with Gmail or Microsoft Exchange, so via Fileboard you can send emails and view attachments. All communication will be properly archived.

It is also useful that you can easily attach files from Dropbox to the email and send it in email.