You probably never think you'll need a passport case until that one time you just can't find your passport. Then you realize that the passport could be anywhere and the drab blue colored cover isn't going to be very easy to spot. When you do have your passport stashed in your purse, it can get ripped and damaged and your passport is one document you should keep as clean and pristine as possible.
The Container Store makes vibrantly colored suede passport cases so you will never lose your passport again. Just slide the passport into the case and the bright colors of the suede will catch your eye anywhere. Stick it in your handbag and the passport will be protected from damage and will be very easy for you to spot.
For a more sophisticated passport case, look for cases made by designers like Tumi. While the prices are a bit higher, the leather cases will protect your passport and make you look like a smart world traveler.