Retail commerce is--to put it politely--limited in Pullman. Most of it is clustered along or near three streets: Main, Grand, and Bishop Boulevard. The nearest Walmart is seven miles east in Moscow (though the more limited Shopko at Grand and Bishop can be a handy alternative for some items), the nearest Costco is forty minutes south in Clarkston, and the nearest Target is an hour and a half north in Spokane. But hey, we've got the same access to the Web and mail-order as everybody else.
And there are some definitely cool businesses in Pullman. I'm going to single out just a few of my favorites.
For used textbooks, try the WSU student bookstore; but for other used books, Brused Books is a great place to shop. Since Pullman has a highly educated population of avid readers, a lot of good stuff gets recycled here.
The punning store name was influenced by the first name of its founder, Bruce Calkins.