One product in particular that I have seen is WalletGuard, which you can get here. Slip this film into your wallet or slip your credit card into the sleeve.

There is a government standard regarding using wallets that are shielded against RFID theft. You can search on "FIPS 201" to find products that have actually been certified to block RFID signals. That's not to say that non-certified products don't work, but it costs money to go through the certification process so many products have not been formally tested. Buyer beware.

The fact that there is a Federal standard that mandates the protection of RFID-enabled documents, like ID badges, passports, etc. certainly means that RFID theft is an issue, but FIPS 201 is for people in certain sensitive jobs or who travel to certain places for their jobs. The threat is a lot more focused for these people than it is for your average Joe walking around with a wallet full of RFID-enabled credit cards.

Again, I acknowledge that RFID theft can certainly be accomplished, I've just never heard of it being a real world problem for average people worried about their credit cards.