[Cdesja5]

Dropbox works well, I've tried "Box" as well but Dropbox is much easier to use. It really works a lot like a computer file folder except it syncs every device the app is installed on. I especially like it on my Android tablet and phone used with Aldiko and Aldiko Sync which uses Dropbox to keep all your devices synced with the same books and at the spot you left off reading.
On my iPod, opening an epub in Dropbox gives me the choice of opening the book in Stanza, megareader, Bluefire or Apabi (I prefer Stanza). Tap your choice and the book gets added to it without any else to do.