Over Christmas I worked on making yet another short url service - Metamark.net. You can use it to convert long and unemailable urls like http://www.fourmilab
There are also a SOAP, a XML-RPC and a very easy to use REST API. And of course bookmarklets you can drag to your browser toolbar!
The site is all XHTML and CSS, but I haven't checked if it validates lately. I have tested it in Mozilla on Linux, Chimera on OS X and of course in links and lynx. I took special care to make sure it works great in links and lynx. There is more about the geeky things on the about page
I am planning to translate the site to other languages, so please send a mail if you are fluent in some exotic language. I would also like to get examples on how to use the APIs in other languages than Perl.
Other comments and suggestions will also be most appreciated.