Biochemistry - It's a great perspective on life (I'm comfortable in saying I have the answer to one of those early childhood Big Questions, what is life?), and there's something poetic about the idea that the tricarboxylic acid cycle cracks carbon skeletons to make C02, don't ask why.
Nucleotide Chemistry is particularily interesting, there's a real nice overlap between Genetics, Biochemistry, and Evolution in this field.
Evolution - I love the picture of life as being a self replicating divergent pattern. Again, very poetic.
Philosophy of Science - I find the philosophy of science to be very interesting; it deals with epistemology, and skepticism in interesting ways. I love Science with Philosophical Implications; Godel's Theorems and Libet's Experiments.
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The scientist only imposes two things, namely truth and sincerity, imposes them upon himself and upon other scientists - Erwin Schrodinger
Member of the WP Strident Atheists