I've experienced this problem very many times. Thankfully, there are a few good solutions. They all involve using file-sharing services.

<sub>Some of the ones I'm about to list have already been mentioned, but I want to compare them in detail.</sub>

 - [drop.io][1] - very easy to set up (a Flash uploader); up to 100MB; easy to share; lots of privacy controls (passwords, permissions); you can control when your Drop expires; paid plans available
 - [YouSendIt][2] - upload via the website; up to 100MB; not a lot of control in the free plan; paid plans available
 - [Dropbox][3] - somewhat hard to set up (you have to install it once; afterwards, you can just upload via their site); up to 2GB; very private (to view, you have to give someone a username and password)

Personally, I prefer drop.io for quick and easy sharing of files < 100mb.
  [1]: http://drop.io "drop.io"
  [2]: http://yousendit.com "YouSendIt"
  [3]: http://dropbox.com "Dropbox"