Here are two of my favorite sources.

Rainbow Resource Center

1-888-841-3456

Call for a free catalog. It is over 1,000 pages and has great product descriptions. Best prices for new material. I use it as a reference too. If you order $150 of product, you don’t pay any shipping. You might consider going in with others on an order. Also, if you pay with a check, you get 2% off your order total.

Vegsource.com

For used material. This is a vegetarian website, but well-known to homeschoolers who want to buy/sell used books. Scroll down the left column, far down, to find homeschooling section. This is an extensive buy/sell board. Even though one buys from individuals, I’ve never had a problem with it.

I like to go to a local homeschool store, homeschool book swaps and book fairs to get a hands on look. Most of my purchases are non-consumables. I have three children and want all three to get to use what I buy.