The Enterprise theme is performed by Russell Watson, not Rod Stewart.
From this website
1.Mr Lucky
2. Inside the Actor’s Studio (by the same man who wrote the theme for Twin Peaks
3. MAS*H
4. Jackie Gleason’s Theme “Melancholy Serenade” (He couldn’t read music but wrote his theme music.)
5. The Pink Panther (used in the movie first)
widdershins, did you know that Paul Anka wrote the Tonight show theme?
Bosom Buddies.
“my Life” by Billy Joel.
He shoots…he scores. 
Woah! Are you talking about the version made by the two guys from U2? 'Cause I absolutely love that version (and the original as well). I thought it was brilliant.
Hogan’s Heroes. I’d know that whistling anywhere.
Magnum P.I.
That was the exact thing that popped into my mind when I saw the thread title! 
There are a lot of great ones, but Cheers is the best, IMO
Doctor Who (Jon Pertwee/ Tom Baker era)
There are some that have been mentioned that I like (Peter Gunn for exapmple). Still, my favorite:
*Take my love. Take my land.
Take me where I cannot stand.
I don’t care, I’m still free.
You can’t take the sky from me.
Take me out to the black.
Tell ‘em I ain’t comin’ back.
Burn the land And boil the sea.
You can’t take the sky from me.
Have no place I can be since I found Serenity.
But you can’t take the sky from me. *
My favorite, by a very large margin, is the music to the Inspector Morse series by Barrington Pheloung.
Though I can definitely get behind votes for Angel and Mike Hammer.
Al Jarreau singing “Moonlighting” or Joey Scarbury singing “Believe It Or Not” would interchangeably top my theme songs with lyrics list.
Quincy Jones’ instrumental “Streetbeater” (Sanford and Son theme) is excellent, and the extended four and a half minute version is well worth listening to.
The theme from the first season of Monk.
Catchy little tune.
I despise pop tune-ring tones on cell phones, but I’d love to have that one for my cell phone if I knew how to find it and download it.
Nah, the best Simpson’s parody of a tv theme song is of the Flintstones:
Simp-son, Homer Simp-son,
He’s the greatest guy in his-to-ry.
From the town of Springfield
He’s about to hit a chestnut tree.
And then he does.
There was a British series called Star Cops that ran for nine episodes in 1987. The theme song was “It Won’t Be Easy”, written and performed by Justin Hayward of the Moody Blues. Excellent show, excellent song; but I’ll be surprised if very many people have ever heard it.
Yea, verily, and anyone who disagrees can fuck right off - though I do have a soft spot for the original Battlestar Galactica theme, it being the one good thing about an otherwise naff show.
Other themes which are very good but not the best include:
Babylon 5
Stargate SG-1
Millennium
and of course Highlander, though that may be cheating as it used a Queen song.
Gilligan’s Island
It told you the story every time.
I really enjoy the jazzy themes of Bewitched, Dick Van Dyke, the Jetsons, Flintstones, Peter Gunn.
Just reading this thread is triggering my brain with dozens of short minute long blasts of greatness.
Law and Order, the original, has a perfect theme song. Even the variants they use for the imposter shows are still pretty good.
I thought the Futurama theme encapsulated the show’s tone quite nicely.
I also like the theme to Aqua Teen Hunger Force a lot.