I've never seen one- I really don't think they do codes at all. I love Zappos and buy all my shoes there.
You can get a 6% rebate for Zappos by joining Fatwallet.com. I subscribe to Lucky magazine so I get a nice 14% off at Zappos using Lucky Rewards (for subscribers only I think). I also use ebates.com. All no hassle, no strings, check comes in the mail. Gotta love it.
Zappos never has codes Nishi, sorry!