They've got their own trading card RPG. It's called The Mystic Warlords of Ka'a. It doesn't actually exist in real life, but I've heard that some real companies are looking to make a real version of this game. It looks it would be an interesting game to play in real life.
Read about the in-show game at http://bigbangtheory.wikia.com/wiki/...ords_of_Ka%27a
And here's tons of card pics. Not sure where these high quality card pics came from, as this is not a real game. Maybe the art department at the studio that made the designs for the cards for the TBBT show got ripped off? No matter, here the pics are for your entertainment.
Card Backside with Logo
And here's a couple webpages that have a ton of high quality card pics, some overlapping what I've already posted, and some new ones.
Page 1: http://www.spoilertv.co.uk/images/th...20Ka%27a/Cards
Page 2: http://www.spoilertv.co.uk/images/th.../Cards/page/2/