Originally Posted by JoeD
The kindle app is on most devices and platforms now so it's perhaps the closest you'll get. Unless you have more than 5GB (I think that's the limit) of non-amazon bought ebooks, in which case it's not going to offer enough.
I know Amazon lets you buy online storage space for personal media files but I'm not sure if the online Kindle reader can access that part of your account.
Me, I'm definitely in the offline camp, so I've never tried it.