I have some I made myself similar to JackBeds, but I tend to prefer these:
http://refsworld.com/index.php/english/wallets/refsworld-rw-pack.html
http://refsworld.com/index.php/english/wallets/referee-match-cards-re-usable-6-pack.html
Last for ages, completely waterproof and you can get 10-12 games out of each side of a card. Use a ballpoint pen, and to clean them simply spray with deodorant and wipe off.
My biggest problem was always reading my own writing after the game!!!!!