https://www.box.com/signup/o/dell_50gb_give_get
Box, one of the oldest, larger cloud storage service provider have this moment special offer: 50GB (usually only 5GB) free storage.
It supposed to be "Dell exclusive offer" but as it seems Dell only sponsor it and everyone can get it. There's limitation however. The biggest uploaded file size for free account can be 250MB so not suitable for bigger backups. It could be still handy to have one.