Jimmy Cliff’s You Can Get It If You Really Want
I’d have John Barry especially compose one for me of course, but meanwhile I’ll use the part of t he The Lion in Winter Suite that begins at 8:15 in this clip.
I’m also partial to the theme to HBOs Rome.
Meatloaf-Dead Ringer
or
Donovan-Intergalactic Laxative
Meatloaf-Dead Ringer
or
Donovan-Intergalactic Laxative
Radar Love - Golden Earring
and from The Good, The Bad, and The Ugly soundtrack, I’d have to go with “Carriage of the Spirits”
I’m changing my answer to Winchester Cathedral. In addition to being memorable but not overused it was thenumber 1 songthe day I was born.
Either “Peace of Mind” or “A Man I’ll Never Be” by Boston.
Or maybe just John Lennon’s “Imagine.”
You May be Right by Billy Joel. Gets both sides of my personality right on the money. 
Probably the closest thing I have is NQ Arbuckle’s “Don’t Remember Me.” Mostly for the lines, “If you’re so fuckin’ clever/what’re you doin’ with me” and “Don’t you ever stop talking?/Don’t you ever fall asleep?”
Or, if you want a song that I can actually link to…The Apologist, by REM.
Dr. Hook: Millionaire
My first choice was Everybody Loves Me (But I’m Paranoid) but I couldn’t find a link to the song.
My theme song has changed over the years. It used to be “Real Wild Child (wild one)” by Iggy Pop. Now it’s “Everything I Do I Do It For You” by Bryan Adams. What can I say? I live to serve!
“Much too young (to feel this damn old)” by Garth Brooks.
Don’t know what one would use a “theme song” for, when I go to baseball games I see the players have theme songs, though. I’ve told myself if I ever get to be a baseball player that requires a theme song, there is but only one choice: Entrance of the Gladiators - really the best choice on oh so many levels.
Splendora, You’re Standing On My Neck (aka, the “Daria” theme)
The Benny Hill theme song.
A couple of my friends and I got hooked on Arrested Development, so of course whenever we get together nowadays, our theme song always finds its way into the music playlist.
For those of you that are link-averse, the song is The Final Countdown by Europe.
I’m disappointed. I thought it would be Mr Wendell.
As a “real” woman, I’d have to go with “Got to Be Real” by Cheryl Lynn
Solsbury Hill, which I utterly want played at my funeral.