If you need to store files online for sync or backup purposes, there are a lot of services available to you.

Dropbox, SugarSync, Box, Amazon Cloud Drive, Acrobat Cloud Drive, Microsoft Skydrive, Apple iCloud, or Google Drive offer a couple of free gigabytes for storage.

If you have security in mind, you may also think of wuala, SpiderOak, or hubiC.

Last but not least, you can make your own cloud with... owncloud.