I have a Suica card sitting here on my desk. Suica is Japan Rail's refillable, tap-payment system. It's been adopted for use at convenience stores and seems to be all over the place now. Basically, anywhere likely to make small sales to commuters is extremely likely to accept Suica.

http://en.wikipedia.org/wiki/Suica

The Wikipedia article mentions the VIEW card, which is a hybrid credit card and Suica.