Same thread gave me the idea for the replayable games thread.
I've rewatched all the Star Trek series many times. I've been slowly rewatching them with my girlfriend. Currently on season 2 of TNG.
Other TV series I've enjoyed rewatching at least once are DB and DBZ, How I Met Your Mother (minus the last season), Avatar The Last Airbender, and I'm sure more I can't think off the top of my head.