I recently had a case to share a few free eBooks with a friend in Europe. The files were large enough that sharing over email wasn't practical. My friend introduced me to Dropbox, a service that allows me to store up to 2GB of files for free, and I can designate a folder to share with him (or others).
Dropbox goes beyond just file sharing though. With their client application (Windows, Mac, and Linux), I can have my Dropbox folder sync across computers. Therefore if I add a file on computer A, it will automatically sync to computers B and C. And if I want to access one of my files from any computer, I can just login to Dropbox and get to my files.
Now that I've used Dropbox for a few weeks, I have detected one thing to be cautious of. It has a feature to perform a LAN check -- before sync'ing out to the Dropbox servers, Dropbox checks your LAN. This is an optional feature, that defaults on. What I found is that it though my WAN connection was part of the LAN, and it significantly impacted my throughput on the WAN. This one issue aside, I've found the application to work as advertised.
If you like the service and want more space, Dropbox offers services that provide 50GB and 100GBs of file storage. You can also get 250MG of additional space through referrals.