What is a good stretchy bind-off for 2:2 ribbing?
I recommend a variation of Jeny’s Surprisingly Stretchy Bind-Off (JSSBO) explained here over at Knitty.com. An additional resource for this technique is this drawing provided by Interweave:  

The drawing demonstrates the JSSBO technique in a k2:p1 ribbing pattern.  To use JSSBO for binding-off a k2:p2 ribbing, such as the one shown below, simply apply the knit-type and purl-type techniques described in Step 1–>Step 2 in corresponding fashion upon the k2:p2 stitches of the ribbing.  (Therefore you could use this bind-off on any ratio of ribbing!)

As you can see it is a nice looking bind off: