I recently posted about PURLs, the venerable OCLC service for providing persistent, and incidentally shorter, URLs. If it’s the shortening feature you want, and if you use Firefox (and who doesn’t?), you may be interested in the Firefox extension W3T URL Shrinker. Once installed, you right click on the page you want a short address for, choose “Shorten this URL” from the context menu, and up comes the brief address.
You can find it at a very long URL, or at http://w3t.org/?u=2yc