Best fundamental books?
For fundamental mammalian cell biology, and molecular biology, and fundamental biochemistry: "The Molecular Biology of the Cell" by Bruce Alberts and colleagues.

It is mostly written for first semester students at university and thus summarizes the basics in a very clear way. Moreover they state whenever findings have some ambiguity, and they use many nicely drawn pictures to convey abstract concepts.  Despite its approachability it covers most fundamental topics of many domains (also diseases).

While the ~2,000 pages of the complete edition might seem a bit intimidating they rarely provide unnecessary detail, and the individual chapters are written in a very concise way (even allowing you to skip some of them).