I love playing Munchkin, but haven't found a good way to protect the cards. So, how do you protect your beloved Munchkin cards?
While I hate the Munchkin game...
the cards are of one of the standard card sizes.
Mayday Games makes sleeves intended for card game play. In about 100 hours of play, I've shed 2 sleeves on my dominion set, and both of those because someone riffle-shuffled lengthwise. You'll need to shuffle sideways, rather than lengthways, but sleeving the cards is your best option. Their data sheet says the purple size are correct for Munchkin, and the green size for Munchkin Quest. It also says you'll need two packs per munchkin 168-card box.
Munchkin cards are one of the standard card sizes so you should be able to pick up some card sleeves at a LGS or big-box store even.