I discovered as a Prime Member, I have unlimited access to certain shows/movies to stream for free. Sadly, they don't seem to differentiate between what's "free" and what I have to pay for. I figured I'd add the few shows I've seen for free and let others add what they know of, too.
Scarecrow and Mrs. King
I Love Lucy
The Andy Griffith Show
Petticoat Junction (theme music replaced on the freebies)