The American Council on Exercise.

The American Council on Exercise offers lots of information for the general public which is nice to see from an organization that also offers certifications that cost a decent amount money. You don't see this information being offered by the other certification web sites and it is unfortunate that they arent willing to share as much information as this website, but I guess that is their own marketing scheme. Although I do not have any certs through ACE I still highly respect the information that they offer to health professionals as well as the general public. Their site is always updated monthly, and they have great guides to go through many exercises at many different levels. So if you're interested in general health when it comes to fitness, I highly suggest visiting the site.