Dropbox is a cloud computing service which can sync filed between Windows, Mac OSX and a Linux personal computers, and make those files retrievable from Android, iOS or BlackBerry device or any web browser.
Dropbox gives you 2 GB of online storage free, and you can earn up to 8 GB more making referrals at the rate of 250 MB per successful referral. If someone referred you to Dropbox you both get an additional 250 MB. You can also buy more online storage.
There is another way to earn more storage from Dropbox. You can complete some Twitter and Facebook related tasks and earn another 640 MB of storage at this link.
All in all, you can get 10.6 GB of free cross platform online storage from Dropbox. Here is a link to the Dropbox website. Give it a look.