As a stay-at-home mom in a one-car family, I do most of my education shopping online. The following is a sample of the great resources out there for homeschool moms like me. I also highly recommend Dollar Tree, the dollar store franchise, as they generally keep fabulous and colorful learning posters, reward coupons, wide-lined paper, flashcards, and other great teacher resources.
Love to Learn - Support this homeschool mom of seven children, who's been in the game for 25 years and provides a great selection of books, toys, and art supplies in her catalog.
Sonlight - Christian curriculum with an international world view. There's nothing narrow about their scope and sequence. At their online catalog, you can purchase entire cores (social studies and English) and add on math, science, etc. They also have a lovable selection of books if you're just looking for a few. A great company who is always trying to outdo itself for customer support.
Amazon.com - We buy enough books to justify paying for Amazon prime which gives us free shipping. If they don't have the book I'm looking for, I check goodreads.com, search the book, and check their list of retailers (you can even price compare).
Oriental Trading Company - This great bulk shopping center has also tapped the teacher market. I especially love their charts and storage solutions for managing all that paper and information.
Obviously not a comprehensive list. I'll add as I discover new resources that make my book-loving heart swoon. Happy Shopping!