TV themes I like mainly consist of TV shows from the 70s and 80s that I enjoyed as a child, such as:
The Jeffersons
Good Times
Three's Company
Laverne & Shirley
The Muppet Show
The Golden Girls
The Greatest American Hero
The
Eight is Enough theme sounds dated now, but it's actually a lovely song.
Eight Is Enough Theme Song
I think I'm probably the only person who remembers it, but there was a short-lived show in the mid-80s called
All is Forgiven that had a theme song that I enjoyed so much that I was (and still am) bummed out that the show didn't last.
And what gay man can forget the theme song for
Wonder Woman?
http://www.wonderland-site.com/html/miscel/soundsd.htm
The Wonder Woman Pages: Audio Lounge
And now for some sci-fi favorites:
I recently said in another thread that I love the theme song to the original
Battlestar Galactica.
YouTube - Battlestar Galactica TV Series Intro 3
I also really like the theme to the miniseries,
V: The Final Battle.
http://thevisitors.info/downloads/music/v-the-final-battle.mp3
The opening to
The 4400 not only includes a beautiful theme song, "A Place in Time," but is visually gorgeous--each shot could stand alone as a piece of art photography. If there were an Emmy for opening credits, this should get it.
YouTube - The 4400 - Opening (Amanda Abizaid - A Place in Time)
I collect variations on what is my personal favorite theme, Dr. Who, by Grainer and Derbyshire. It is supremely eerie in the earlier variations, gaining power and depth, then veering into the silly, then right back on course with the current doctor. Not bad for a show that's 45 years old. I just love how it has evolved and how wonderfully it fits the show.
I can't say it any better than that. I've been on a Doctor Who kick lately, with the 4th series of the current show wrapping up recently, and also watching old episodes on YouTube. I love the theme from the classic show, particularly the older versions. (The synthesized 80s version seem dated now and, as you say, a bit silly...but I loved them at the time). But the theme for the current show, combining elements of the original with more traditional instrumentation (drums, brass, strings) kicks ass.
You can have loads of fun (and/or drive yourself crazy) "composing" your own Doctor Who theme with different pieces of the theme from the classic series.
BBC- Doctor Who - Radiophonatron