The theme song for the comedy-mystery show "Psych" is fantastic -- it perfectly and humorously sums up the show and the relationships.
It helps that the song was written and performed by the show's creator and his band (which existed before he created "Psych," as did the song itself! It just happens to fit the series ideally.)
"In between the lines there's a lot of obscurity/I'm not inclined to resign to maturity..."
https://www.youtube.com/watch?v=NLhKymGr-EY
Best of all, "Psych" would alter the theme song to fit specific episodes!
--Sung fantastically by Boyz II Men for an episode about a men's a cappella singing group.
https://www.youtube.com/watch?v=gGGzzZyJECE
--Sung in Hindi for a Bollywood-themed episode.
https://www.youtube.com/watch?v=LbodxiyYAHw
--For an episode homage to "Twin Peaks," the theme was reimagined and performed by Julee Cruise, who did the original "Twin Peaks" theme music.
https://www.youtube.com/watch?v=fyIxUWl0U3M
--In Spanish for a telenovela-based episode.
--Creepy horror movie version for an episode based on "The Shining."
--And several more, including a Marvel-like orchestral fanfare version for one of the "Psych" TV movies in recent years.