with humyo.com. Up to 10GB storage, free forever. 5GB for media, and another 5GB for non media. There's a commercial version as well at £46.99, though at that price I'd think about investing in an external hard drive, unless off site backups are really important to you.
gathers all your valuable digital stuff — photos, documents, email,
music, videos — from all your PCs and laptops. It backs up everything,
securely stores it, and organises it all so you can find or share your
files from anywhere.
Dropbox.. is now public, so you don't need an invitation code. It's a piece of software that you download which allows you to backup files as you change them. I've not tried it myself, but it does look very impressive.