I used to run an IRC robot called shorten that'd scan the channels it was on for long URLs and shorten them using Metamark:http://metamark.net/
Not using IRC I'd forget to keep it running, so it's not much use.
If you'd like to volunteer to run it, send me a mail and I'll point you to the code. :-)
update - Tod McQuillin
foolishly generously volunteered. Thanks Tod!