They offer 5G free space. Comparing Amazon (5G) MS SkyDrive (7G space) DropBox (2G) and Google (5G) to iCloud, iCloud is useless except for backing up iDevices and specific Apple files, Pages, Keynote etc. Hopefully they make it more than a castrated MobileMe someday.

So between the first 4 you can have 19G of free off site backup, pretty cool. Google will soon have iDevice support. Amazon is the only one that doesn't have it, yet. They have it for android but not apple devices. Amazon does offer a streaming player app for the iPhone but no file storage access yet.

Those are just 4 off the top of my head. I can't even keep up anymore.