BookBook from Twelve South
Twelvesouth.com wants you to put your money where your phone is. With BookBook ($60), a cool little wallet / phone case, that lets you combine the two since you never leave home without the two of them. Made exclusively for iPhone 4. This little book has a convenient ID window and slots for your debit/credit cards and cash. Instead of grabbing your wallet, phone and keys when you walk out the door, simply grab BookBook and your keys.
Buy now: $60