Now, mind you, this is not to say these are the ones you should leap straight into promoting! For one thing, competition is extremely fierce, and a few are considered by Google (and the rest of the world) to be on the shady side – so shady that various online sites such as Squidoo have banned certain subjects altogether. (Two of the “banned” ones would be Acai berries – a proven scam – and gambling links.
Avoid those like the plague!)
However, you are certainly not limited to the above category list! If you research and find a lucrative niche, or you are an authority on one that has nothing to do with the above, by all means, find CPA offers that focus on your unique market.