My URL shortener, Surl, which is located here now has Ubiquity support. Hit the page, and if you have Ubiquity installed for Firefox, it will recognize the command and you can subscribe to it. In Ubiquity, you can then use 's.darkhax' (which will complete sooner due to the fact that there aren't many commands with a dot) to shorten URLs. It replaces the highlighted URL and copies to the clipboard.
Check it out!