Newton Philosophical Writings
From the Closed World To The Infinite Universe - Koyre
Physics - Aristotle
Meditations on First Philosophy - Descartes
Correspondence - G.w. Leibnez and Samuel Clarke
Discoveries and Opinions of Galileo -
Selected philosophical Writings - Francis Bacon
Prolegomena to Any Future Metaphysics - Immanuel Kant
An enquiry Concering Human Understanding - David Hume

$65 if you buy the whole bunch.