The Quirkles' Web Sight.
We also have used an online system called Super Charge Science. This was a more intense and advanced series of lesson and we did not stick with it due to it being a bit over my son's head developmentally. It's still very good and has so much to offer. I had issues with loading the videos and also there was so much reading material that was far to advance for my student. We may go back to this source in coming years. It is very complete.
Sciencelearningspace/ Super Charged Science
Another venue we use is the Arizona Science Center's homeschool classes program. These courses are taught by Mary Katherine Campbell a certified teacher. At least once a month we attend a classes that can range in content from Simple Machines to Insects Study. Last week was by far my son's favorite as it was a class on organs. My son was able to dissect a cow's heart, lung and kidney. Nothing like project bases learning to give hands on synthesized experiences. We watched as a Professor from ASU hooked a shop vacuum up to a cow's respiratory system. The lungs and trachea were all kept in a plastic bag to keep it neat and tidy. So the teacher fit the hose of the vacuum on the trachea ( it fit perfectly) and the lungs filled up and the children got to see how and feel the process of full and empty lungs. The kids love it, I could not help wondering how this experiment was conceived. I picture grad students in a lab, late at night fooling around with a cow's lungs and the shop vacuum. Someone figured out the hose of a shop vacuum fit perfectly on a trachea.
After the cow lung and vacuum experience we move on to the organs. Conor was skilled and curious. He had several tools but preferred the little sharp scissors. I am squeamish and not the best lab partner on dissecting day but I dealt with it and helped. Conor was amazing and he rocked. I kept my self together. It was a good day with guts. We go back again this year for pig's eye and rattle snake dissecting classes.
Another science homeschooling resource for us is Mr. Q. at http://www.eequalsmcq.com/ He covers K-8 in Life, Earth, Chemistry and Physical Science. Eh also has some advance studies for High schooler's in Biology, Anatomy and Physiology.
All our favorite links to cool free things.
National Science Foundation resources K-12
http://snap.berkeley.edu/ programming with blocks
BBC UK schools resource link
Maker's Camp Google + community
We also watch TED Talks and many You Tube videos on science. There is so much out there for free if you google search for it and are curious.
My Pinterest board for Science has some fun stuff on it as well.