ADrive offers 50GB of online storage space for free. (Be sure to select the "Basic - Free" plan.)
That's one of the largest storage capacities I've seen from a free service. ADrive is compatible with Windows, Mac, and Linux; for more information on this service, click here:
http://www.adrive.com/plans
EDIT: It uploads complete folders with subfolders containing all the files. I find it a good way to backup important stuff incase if you need and if you are on the move.
Whynot Dropbox?