Wow, from Plato to Polya, this venerable work looks very very much like it is worth reading, taking notes, and reading again just for the pleasure of it, once I actually have time to enjoy all of the citations (like the Myth of Euclid?! and Chinese mathematics!! -cool!!!).
I so enjoy the study of teaching mathematics, pity I don't enjoy the students nearly as much, the vast majority of the time (ok, nearly all of the time, but I do enjoy planning my lessons!).

And let us not forget Pacioli, of double-entry book keeping fame, no?