There's one website in particular that I use regularly but haven't given much thought. I almost take it for granted that everyone knows about it. It's Rapidshare.de. Take a look at it yourself, you'll see why it's so great.
It's a fast and easy way to send files to people, without needing email addresses or setting up direct connections in P2P programs like Limewire. Their FAQ will do a better job describing it than I probably can; basically, you enter the path you want to upload, and it it returns a download link you can distribute.
There isn't much more to it. Rapidshare is simple to use, and effective. Like me, you might not see a need for it, but once you try using it you'll realize it's more useful in more places than you'd expect.