Favorite (for now):
Community
Least favorite:
Little House on the Prarie
(Reminds me of being stuck at my babysitter’s house after school).
Another favorite:
The Simpsons
Favorite: The Big Bang Theory - This is longer than the clip they actually use on the store.
I can’t think of a least favorite - I block those from my memory 
I knew someone would bring up The Big Bang Theory.
It is a good one! Barenaked Ladies rock!
Favourites (not all of these were written specifically for the show):
The Simpsons
The Nanny
Seinfeld (more “theme music” than a “theme song”)
Jonathan Creek (an arrangement of Dance Macabre)
Absolutely Fabulous (love the Pet Shop Boys-produced spin-off single too)
The Wire
Rage (an Australian late-night music video show which uses a distorted sample of an Iggy Pop song as their theme, it’s hard to explain but it fits perfectly)
Least favourites I’ll have to have a think about. While I love the show I could easily go without hearing ‘I’ll Be There For You’ from Friends ever again.
My sister has an extreme hatred of the Green Acres theme song.
The Sopranos (favorite)
Another Least favorite:
The theme from the late, great Terriers (sob). The shorter version of Gunfight Epiphany used as the theme is here. The full version of is here.
Favorite-The original Littlest Hobo
Least Favorite-Blossom
The Beverly Hillbillies!!
Truly a classic!
Also good! (not a TV theme song though)
Favorite: “Firefly”
Least Favorite: “The Flintstones”
Regarding “The Flintstones,” fossils like me will recall that the show did not originally end with the “Yabba Dabba Doo, gay old time” song associated with the show. For at least the first season, there was a low-key instrumental theme, which was strongly reminiscent of the Bugs Bunny “Overture, Curtain, Lights” song. I’ve often wondered if that similarity may have had something to do with it’s replacement, or if it was just the fact that it was boring.
Old The Flintstones
Does sound like Bugs Bunny! (http://www.youtube.com/watch?v=YdVseljx2UU )
Never liked **Firefly’s **though… I loved the show:
Wow, I didn’t even remember to think about that one!
Another good one:
Duck Tales
Favorites:
Darkwing Duck
Firefly
Battlestar Galactica
Kim Possible
The Boondocks
House (not a song, though the music is from a song)
I know I’m not the only one around here that loves The Greatest American Hero theme ( including George Costanza’s version). My personal favorite, though I may be the only one who remembers it ,is Electra Woman and Dyna Girl.
My least favorite is Night Gallery. Holy cats did it scare the livin’ crap out of this latch key kid.
Peter Gunn
Mission Impossible
Twilight Zone
Six Feet Under
Mad Men
Deadwood
Sopranos
Favorite:
I always hated the theme for the Sopranos.
One of my favorites has always been Twin Peaks. I watched the entire series on DVD, twice and I don’t think I ever skipped the intro. Part of it is because I like watching the giant saw blade getting sharpened, partially, because the show was so good that watching the intro really got me into the right mindset for the show.