In 2008, Uruguay issued a postage stamp commemorating the International Day Against Child Labour with a picture of a Plan Ceibal child with an XO laptop. Back then, I bought several of the stamps and gave them away as gifts. Now you too can buy an OLPC stamp from Uruguay, courtesy of eBay seller CollectorBazaar_2009.
Note that this stamp is unused. You also have the option of buying a canceled OLPC stamp from June 12th if you want greater commemoration of this philatelic event.
Whichever you want, hurry up and buy them fast - they'll be gone quick (if not already).