Recently signed up for Microsoft Office Live Workspace beta. This gives you 5gb free online storage, and a usable web interface for accessing and sharing the files. The only downside is that you do have to have MS Office installed on a machine in order to edit documents (other office suite clones will not work). The nice thing is that since the documents remains ‘pure’ your formatting won’t be messed up. I’m currently using Office 2003 (which I prefer to Office 2007) and it works great! You do have to wait for files to download and upload, but in most cases this is trivial.
Unfortunately, Microsoft only allows you to use the space for Office-type files (and inexplicably, jpeg files, and possible other graphic files). I guess they are getting wiser.
Check it out at http://workspace.office.live.com (Inexplicably, this is currently working for me in Firefox, but not in IE. This will probably resolve itself.)