With Twitter and other short message services, the number of link-shortening services seems to have exploded.
Kevin Marks explains that not all services are created equal. Some use a 302 redirect that leaves open the possibility the URL may change in the future.
All journalists should have several link-shortening services in their utility book marks. I like NotLong, especially because of its comparison table that leads to some of the other leading ones. But now that Tiny URL gives you the option of naming the links it creates, I've been floating back there.
If you want a staggering list, here's the DMOZ directory, but I make no promises these work or are serviceable.