I've been using Dropbox for a while now and I've been impressed. You get 2 Gigs worth of space free and Dropbox will install a folder (by default it goes into "My Document") and whatever files you put in there Dropbox will also put them on their servers. You can then access the files anywhere online and it will automatically update the files when you revise them.
You can use the "Public" folder that it installs like a free FTP site for large files that you can't e-mail.
You can invite people to share any of the folders you create so they can see the files also (like photos, video, etc).
Just having it to backup your improtant files is awesome. Anyways, if you use this link you'll get 250 meg on top of the 2 gigs (and I will too):
http://www.dropbox.com/referrals/NTQ5OTIzMDg5
Post if you have any questions and or read the FAQs on their site.
Cheers,
Ben Lund