Chains Invent Insanity is a Cards Against Humanity answer card generator. As the name suggests, it generates cards based on a Markov Chain compiled from a wordlist. This wordlist is comprised of every single (official) answer card ever written for every edition of the game.
A service that will print high-quality stickers, business cards, and what have you out of images that you send to them. Their prices are quite reasonable, also.
Count Zero's article on magstripe reading/writing reprinted in the sci.electronics FAQ.
Create your own badges and ID cards. Not really official looking, but gamers will find it useful for making prop ID cards.
MPC is a company that prints custom decks of cards (54-234 cards per pack) in multiple sizes. You'll probably want to buy in bulk to get a decent price. People tend to use this service for their aftermarket Foo Against Humanity decks.
A website and Youtube channel for stage magic and prestidigitation. Specializing in close-up stuff, like cards and coins.
A utility that reads the data from magstripe cards and tells you what's on them.
A site that lists every creditcard vendor and their Cardholder Verification Methods for the cards they issue. The site seems to be crowdsourced because the companies don't necessarily publish this stuff.
A company that prints custom playing cards in small batches. Will even print single decks of cards at a good price. Download their template file prior to sending an order.