I'm using this site to advertise Dropbox. For one, because it's really useful if you want to share large files with friends or have multiple computers yourself, and secondly because the more people I invite, the more space I get. If you sign up for Dropbox after getting invited, you and the inviter both get 500 MB extra.
If you don't know what Dropbox does, it offers at least 2 GB online webspace, for free. You can install the Dropbox app to get a Dropbox folder that will get synced to all your computers, and most smartphones and tablets. In addition, you can sync selected folders with friends or upload files to a Public directory so you can give the file's link to people to download.