Kolossal Killer by Kenton Knepper is one of my all time favorite effects in magic. At any time, you can have a random spectator name any card, and then BAM, that card is in your wallet. It is simple, clean, and impossible.
When I first purchased KK, I looked at it, and then threw it in the junk drawer. The method seemed way to simple and I didn't think it would fool anyone. Boy was I wrong. About a year later, I pulled it back out and decided to give it a try. I instantly got killer reactions and because of that, it hasn't left my wallet since...and that was about 11 years ago.
For those of you who are looking for the best style wallet, this is my current go to for KK. It is called the Big Skinny, and I love it because in my experience and the method, you want the slimmest wallet possible. This has enough pockets to do the job and also hold a few other items. I currently have a whole magic show in this wallet that I always have on me.