Dropbox is a file hosting service operated by Dropbox, Inc. which uses cloud computing to enable users to store and share files and folders with others across the Internet using file synchronization. There are both free (2GB) and paid services, each with varying options; the service is cross-platform, with client programs available for several different operating systems as well as a Web-based client.
To get a free dropbox account (and help me to get more free space) click here
There is also an iphone application available.
An interesting article about dropbox and three major competitors for secure cloud storage can be found at https://www.cloudwards.net/dropbox-competitors/