PassSource is a website that allows you to create a Passbook card without the need for an app. The site currently has template inputs for around 50 vendors and the list is growing. The list includes businesses such as Subway, RIteAid, Best Buy, Amtrak, AAA, Gamestop, Costco, and many more. To create a new Passbook card fIrst point your iOS browser to http://www.passsource.com. Once there, select "Create", and you are on your way to creating new Passbook cards. The templates for vendors who have store locations have the ability to search and enter in a local (favorite) store. After selecting a store (not required) you then input the rewards card barcode information and/or identification number. Below is a sample of the Rite Aid Wellness+ card.
If you want to try out Passbook and you are a patron of a particular business that is currently supported by PassSource, I would highly recommend going over to http://www.passsource.com and give it a whirl. I know I have and it's made Passbook that much more useful to me.