Philosophy
Although Hume's classic Treatise on Human Nature is a key work of political philosophy to come out of the Scottish Enlightenment, Hume's forgotten masterpiece Of the Standard of Taste, in which he argues that judging art is not arbitrary, is probably the most important work in aesthetics before Kant.
The extreme degree to which Voltaire was hated by the great men of his era is surprising--hated even by the likes of Mozart, who wrote to his father after Voltaire's death, "the arch-scoundrel Voltaire has finally kicked the bucket."
Socrates' speech on love in the Symposium--arguing that love is merely a longing for immortality and ideas are immortal--is just a conceit of the intellectual. I prefer Aristophanes' speech, imagining a world in which humans were once four-armed, four-legged, and two-headed balls who tumbled around doing cartwheels, each one split in two and yearning to find their other half.