Pretty much any decent science fiction will have a dose of poly in it. Much of it more than a dose. My personal favorites are, of course, the Heinlein books--- The Moon is a Harsh Mistress should be required reading for all newcomers to poly.
I'm also a big fan of Farscape, and Season 3 when Aeryn has to choose between two clones of Creighton really rings the poly-agony bells. More recently, Caprica depicted a poly family as being the most normal thing in the world and didn't even bat a critical eye. They just introduced the character, and her husband, her other husband, her third husband, and all their wives, as if it was all perfectly normal, which in their society, it apparently was.
There's a lot of crossover between poly and SF. Want to find a poly couple to date? Go to an SF con.