We have a local teaching store in my town, but I haven't found a whole bunch of things that I need there. For one, I couldn't find anything on evolution, and the owner said she couldn't even find anything through their suppliers either. I live in Georgia if that explains anything. So we use the internet and our paltry library.
I started using the same textbooks the kids had been using in school. I just bought them on eBay and on Barnes and Noble. They have a used book section, and the prices are really good.
I never found a curriculum I liked. The "one size fits all" approach doesn't work for me, so I designed my own. I started with the state standards for each subject and would purchase whatever I needed to meet them. Of course, we go above and beyond the state standards, but almost every curriculum I saw was religious in nature or was not as advanced as I would like.
Edhelper.com has been invaluable for me. They have literature units that allow you to print tests for the books your kid reads. There are also so many other subjects and materials for each that you can use. It only costs about $20 per year for the subscription, and you have unlimited access. I did order the full subscription since my younger kids read the high school-level books. That was only about $30 for the year. They constantly add new materials, and you can add writing prompts to tests or customize them however you want. Or you can just print the one they make for you.
Here is a list of a few websites we use. Some of them have online tests and tutorials:
Math.com,
NCES Kids' Zone Home Page,
Education 4 Kids, Inc.,
funbrain.com Grammar Gorillas
I couldn't homeschool without the internet!!
I also use interactive Cds and DVDs, including multimedia algebra, the human body, etc.
I also encourage my kids to do independent research. For example if we are talking about Pre-historic man, and they ask a question, I get them to find the information and to write it up, with sources, and present it to the rest of us. They are 9, 11, and 13, and this helps them in many other areas as well.