There are various online science courses available for homeschoolers. Sometimes it's much easier to view an experiment online and then do your own experiment rather than trying to do it on your own first. Some of these courses are curriculum for science that is offered online and other sites are mostly experiments.
Monarch Online - This is a newer program produced by Alpha Omega Publications (AOP) that is all online for grades 3-12. They not only offer Science but all the 5 core subjects along with many electives.
Learning Grace Academy offers several schools that are all online that each offer science courses within their curriculum. The schools are Grace Academy, Jubilee Academy, Morningstar Academy, and Southern Baptist Academy. You will want to decide what you want in an online school and then look at each of these individually.
Supercharged Science - For those of you not wanting a full curriculum package and just strictly wanting pure Science, then Supercharged Science is the best of the online science courses available. They offer a great balance between videos showing science experiments and curriculum that supports what was learned in the experiments.
We have been using this program the past 2 years and just love it. I can put my son in front of the screen to watch the video and he watches with great interest. Then we can either do the experiment ourselves or just talk about it. I'm really bad at doing experiments. They never work for me. The lady who does the experiments is Aurora Lipper. She is a scientist/mom who speaks to kids in very plain language but you KNOW she knows her stuff because her experiments are not just simple things like how to mix sugar and water together. They have really done their homework here and have lots of helps for parents on how to best teach science.
You can see my interview with Aurora at Supercharged Science and get all the details about how to get their experiments available on your computer too. They believe that students should do experiments first so that they get excited about science and then they will be interested in the curriculum and want to learn more about how and why things happen. If you think about how the great scientists became great, you will realize that they did experiments first and then investigated how and why things happened the way that they did.
When looking for online science courses it's important to decide what you want first. Do you want your child to just complete a textbook or do you want them to be excited about science or at least have a good idea of what is going on in the world around them?