SimpleK12 is a great site that has a tremendous amount of resources for educators. They offer online professional development, curriculum resources, assessment ideas, free downloads and resource kits and resources through their blog, I Love EdTech.
SimpleK12 is also know for their bunny slippers! They promote their online offerings as a way to learn while in your pajamas and the bunny slippers have become their symbol. I was chatting with some of the SimpleK12 staff at ISTE2011 and they were all wearing their bunny slippers.
SimpleK12 has great resources, provides free webinars, student curriculum for educational technology, and has a great staff that is friendly, responsive, and knowledgeable. They have different free e-Books and other services available, including fee based professional development.
Follow them on Twitter, on Facebook and even check out their YouTube channel.