I know people mentioned Lord of the Rings, but there's also Luthien/Beren and Tuor/Idril in The Silmarillion for the Human/Elf pairing. And if you venture into the fandom, there's plenty of cross-species stuff.

Human/Cyborg (I don't think anyone has given you any examples for this yet): Blade Runner, Ghost in the Shell (with extra genderfuckery subtext!), and Chobits.