How to cheat at cards
A friend of mine named Brian Brushwood has a youtube channel called Scam School where he shows people how to cheat. I don't advocate cheating but learning how to cheat does give you some defense against people who do.
Here is Brian's webisode about how to make and use a marked deck.
Brian's Scam School has a bunch of cheats. This one shows how to cheat at coin flipping.