I'm not sure I'm digging this style of case for the Passport, but I can vouch for the quality of the stuff WaterField makes. I have their Cityslicker case with brown leather for my 3DS and I get a lot of complements on how "professional" looking it is.
Plus the case is the size of a real passport. If left zipped open you could pull it out of the case from your pocket and keep some cards organized as well. I think I'll take the plunge. At worst I have a nice passport wallet.