They're $40 from Thinkgeek, perfect for doing Downward Facing Droid and Bot's Pose. Also Happy Android. 95% cotton/5% spandex, machine washable, sizes S-3XL.

http://feeds.boingboing.net/~r/boingboing/iBag/~3/C6_DXeAHmDk/r2-d2-yoga-pants.html