Most online classes will prepare you to pass the test if you study. I used Insurance-schools. Worked for me. Others have done a classroom crash course. Worked for them. Testeachers is a forum sponsor and some have had success with them. It depends on your study habits and what you are willing to do.
The bigger question is are you sure you want to get into health insurance? Are you looking into the Medicare market or IFP's? Do you have something lined up to work the health insurance market? It can be rough out there.
Health Insurance policies as we know them today will cease to exist if America adopts cradle-to-grave Government run health coverage.
But most experts agree that this would be at least 5 years down the road, if it happens at all.
In the meantime, every American has to have health insurance. The government mandates it and allows licensed agents to contract with insurance carriers who pay us to sell it. There are very few sales careers where people MUST, BY LAW, purchase what you're offering. Get it while the gettin's good.
-ac