Knitty is up! Yaaaay!
Knitty.com will tell you all about how to do this bindoff, called "Jeny's Surprisingly Stretchy Bind-Off."
I used to go to great lengths to avoid binding off -- going so far as learning how to do a k1p1 Kichener stitch so I could graft on a waistband. I generally avoided toe-up socks and other patterns that required a bindoff, losing out on a world of designs.
After I got seduced into the world of making moebii, which are knit from the inside out (unless you want to do a very messy graft) I realized that the jig was up -- I couldn't escape binding off anymore. This sparked a series of attempts to come up with a better bindoff, and this one quickly rose to the top of the bunch. It went through some evolution after I got in touch with (the AMAZING) Cat Bordhi. She helped to simplify and streamline it.