Where does this stuff come from?

Alright, I was watching a TV show last night and they were showing how pills are made. My question is, where do the chemicals that make the drug come from? Street drugs are easy. Cocaine comes from the coca plant, heroin from the opium poppy. Some prescriptions are easy also. Penicillian comes from mold. But, where do these new drugs come from? Like the cancer drugs or AIDS drugs or any of the blood pressure or cholesterol drugs? Are there just millions of chemicals out there and if you mix different combos they do different stuff? Or do most come from plants? If anybody has any links or any insight, please share. And please, no stupid answers.

Here's a good example : Taxol, a relatively new and heavily used chemotherapy drug for cancers, came from the bark of the Pacific yew tree before it could be biosynthesized.
Also, Vinca alkaloids use for cancer and leukemia are from plants. Quinine came from bark. Digitalis was from the leaf of a plant - found in the late 1700s.
Many medical compounds are found in nature just like the drugs you mentioned. Often these are later synthesized.
Cis-platinum used as chemotherapy for many cancers is simply a chemical form of the metal platinum accidentally found in labs to interfere with cellular reproduction.
Thousands of compounds are tested and fiddled with (there's a professional term) to find active agents for diseases. Most compounds wind up as dead end wasted time and money.
We often bash drug companies for their profits, but the profit motive keeps them spending money searching for newer, safer, more effective drugs. [No, I have never worked for a drug company - - just trying to be fair to them.]