I’ve had my Speck Smartflex Case for a month now and I have to say it is super convenient and I haven’t lost my wallet. The main things that are sad are that it completely hides the very nice gold iPhone underneath and you have to be careful with just three cards. But it is a good value. About $25 or so from Amazon.
In looking at more reviews, I found The iPhone 5 Credit Card Case Thread – Page 11 – MacRumors Forums and they talk about the SAFE Bullet Train iPhone case. This stacks five cards and also has a hing for viewing. Might work, but I really like the slender design.
The other good looking case is the CM4 Q Card. At $40, the nice thing is that it is a soft pleather material. Looks nice.