hxxp://www.xylibox.com/2013/02/alina-34-pos-malware.html
hxxp://www.xylibox.com/2013/01/vskimmer.html
hxxp://www.xylibox.com/2012/12/point-of-sale-and-memory-scrappers.html
also check on kernelmode(dot)info and you will see a lot of samples of pos malwares