Nice place to get Japanese food. They have sashimi-grade fish on Saturday every two weeks, but otherwise have frozen fish too. You can also find all kinds of Japanese rice/noodles/snacks/miso paste/etc. that you won't find in other Asian markets in Madison.
As other reviewers have said, what makes this place awesome is the customer service--the lady who owns the store is so nice and helpful, and will be more than willing to explain any questions you might have about Japanese food. She even gave me a free chunk of cooking salmon one day when I was going to buy sashimi!
And yes, they only accept cash, and since there aren't many people running the store (only the lady and her husband sometimes) and she is constantly answering people's questions, it can be a little slow sometimes. Still, Oriental Shop's the only place in Madison I know where you can get sashimi-grade fish, and coupled with the excellent customer service (I haven't had better from any other shop, really), this place is a must-know for those into Japanese cuisine.