I recommend trying Zoolz it gives you 4 GB free storage and it increases with each accepted invitation you send, you will earn 250 MB of free space could get up to 20GB. Cool Right!!!I am currently using it and I find it great and the most important thing to me that it is safe as data centers located on Amazon S3.It does automatic backup. You can check it here: http://www.zoolz.com/
I'd stay away from CX.com.
I was sucked in by the amount of free storage they allowed, but in the process of backing up my files more than half of the files on my hard drive were deleted. I did extensive searching, and they were not moved - they were gone. I emailed CX a half dozen times begging for help, hoping it was part of their backup process and that they could help me easily restore the files. I never got a response to any of my emails, and when logged into my account the dashboard said I had no outstanding inquiries - my emails to tech support disappeared just like my files.
In the end I had to go through 500 folders, each with 3-5 subfolders and many files in each one, to find the stuff that had been erased and individually download them back to my PC. There wasn't even a way to DL the folders with all their contents; I had to DL each and every one, one at a time.
Steer clear, and good luck.