|Image credit: The Fortune Cookie Reader|
Mysterious fortune cards are craftable at 450 inscription, they require a single blackfallow ink and one parchment, the rough material cost for both of these items is about 20g, I've sold cards for as much as 250g/ea, and they sold quickly.
Cold, from Cold's Gold Factory has recently made three excellent tips on how to properly advertise your cards, Mysterious Fortune Cards Bait and Switch, and the post that started most of the hype, Cataclysm Item Preview: Fortune Cards & Fortune Cookies. There is a lot of good info contained within those three posts.
If you're serious about selling the cards, I suggest you go check out the posts above and learn how to properly market them, I've personally made about 15k in one day ( not all was profit, ~80% of it was ) and it was only in a matter of an hour or two of spamming in trade that you by using the cards, you had a chance at getting yourself a nice 5k.
One last thing before I let you go, don't get sucked in yourself. While the cards are promising, people have done the math, and the chances for you to use the cards and come out winning is low, it's like gambling, just at low risk, I don't want you guys growing a habit that isn't good now do I?