* Here's a scintillating grid shirt: http://www.cafepress.com/losethegamesho
* Here's some more on zazzle: http://www.zazzle.com/pd/find/qs-illusi
I particularly like the rotating snake illusion shirt.
* Another snake shirt: http://mistupid.com/shop.php?i=mist
* Here's another shirt which makes clever use of the fork prong illusion.
* Rabbit in Escher scupture: http://www.threadless.com/product/503/I
* Several from the Archimedes' Laboratory store on CafePress: http://www.cafepress.com/mariejo2/22180
* Also, a Stroop Effect shirt: http://www.cafepress.com/buy/grey/-/pv_