There are loads of extensions and bookmarklets that create shortened links from long URLs, but the bit.ly and j.mp services don't need them. Add them with a slash before the URL in your address bar, and you're good to go.
Web PR enthusiast Steve Rubel shared this tip, directly from bit.ly's management, on his personal stream site, and it's a good one. Simply add one of those two services before your URL — j.mp/http://lifehacker.com.au — and you'll quickly redirect to a page with the shortened version of your link ready to be copied or posted to a social network. Handy stuff for keyboard devotees, the add-on-averse, and for when you're working from a browser that's not your own.
One-Step Bitly URL Shortening from the Address Bar [The Steve Rubel Stream]