Extract url from string

Hey guys, I've been banging my head against the wall trying to figure out the right pattern to use to extract a URL from a string using preg_match(). I've been STFW for a while now, and all the examples that I find are for extracting URLs from within a <a href=""> tag. Here's what I need, and I'm sure it's quite common, especially with forums etc.; hopefully someone has a code snippet they can share. INPUT: This is some text http://www.example.com/page.html this is some more text. OUTPUT: This is some text <a href="http://www.example.com/page.html">http://www.example.com/page.html</a> this is some more text. Thx in advance, -B