Sena WalletBook Case for iPhone 3G/3GS, Croco Tan
This is my second Sena iPhone wallet case and I love it!  In fact, it's the reason I've stayed with an iPhone vs going with one of the Android devices out there.  The fit is snug initially, but with time it does stretch so be careful about taking the phone in and out because eventually it won't be snug anymore.  And if there's not enough room for all your cards just give it a month or so and let it stretch.  I currently have two ID's and three credit cards in mine after a couple months of use.