* Here's a scintillating grid shirt: http://www.cafepress.com/losethegameshop.56969429
* Here's some more on zazzle: http://www.zazzle.com/pd/find/qs-illusion/ps-40/pt-235/st-POPULARITY?sz=1
I particularly like the rotating snake illusion shirt.
* Another snake shirt: http://mistupid.com/shop.php?i=mistupid/mistupid5.8211841
* Here's another shirt which makes clever use of the fork prong illusion.
* Rabbit in Escher scupture: http://www.threadless.com/product/503/Illusion_of_Rabbit_Optical
* Several from the Archimedes' Laboratory store on CafePress: http://www.cafepress.com/mariejo2/221803
* Also, a Stroop Effect shirt: http://www.cafepress.com/buy/grey/-/pv_design_prod/p_709997.9300625/pNo_9300625/id_3697534/?click=true&CMP=KNC-F-ALL