Hostel Pristavni
Unofficial website with information about the Prague Card.
http://www.hostelpristavni.cz/card_eng.htm

Prague Bonus Card
Three cards offering varying benefits.
http://www.prague-bonus-card.com/

Prague Card
A three day discount card that will save you a bundle on transport and entry to the city's museums, sites and galleries.
http://www.praguecard.info/
http://www.praguecard.biz/