It’s something we had to create for our email + Twitter integration last month (which has been used for over 60,000 email campaigns so far).
While working on that project, we just thought "what the heck, might as well make it a live product too." So there you go.
It’s a lot like TinyURL, and it’s even got its own bookmarklet you can add to your browser toolbar, but you can also post your eepurls directly to Twitter, or email them to a friend.
Check out EepURL
See what else is in MailChimp Labs