TeachersPayTeachers is the world's first open marketplace
where teachers buy and sell original teaching materials.
Here's an interesting site where you can find teaching materials. Some are for sale, but many are available for FREE.
You can browse the lessons by Grade Level, Subject, Lesson type, or Price.
and if you want to make some money of your own - you can try selling some of your own lesson plans :-)
Kindergarten Teacher earns $700,000 by Selling Lesson Plans Online