But there was a time -- it still happens today, but to a much lesser extent -- when songs weren't borrowed from popular playlists, but written specifically for a television series. They were designed to make you identify them with their respective shows -- but they're also songs that deserve a listen once in a while by themselves.
(Fair warning: "Suicide is Painless" was written for the movie version of M.A.S.H., not the TV show, which sadly disqualifies it here. Also, the Rembrandts' "I'll Be There for You" is not on this list, even though it was written for Friends, and a huge hit besides. It was a decent song, but then the show lasted for 137 years and you want to kill yourself when you hear it.)