I'll agree with Mission Impossible and Deadwood, but that's about it. I'll admit to a fondness for actual songs as themes (Bosom Buddies, Justified, CSI, Veronica Mars, True Blood)
I really like the How I Met Your Mother theme, because it sounds like the kind of ditty you'd shout along with at a bar.
What else? The X-Files, Firefly, Doctor Who, Blackadder, The Wire, Dragnet, Adams Family, The Dick Van Dyke Show, Knight Rider, Law & Order, The Lone Ranger, M*A*S*H*...
Top Gear, obviously.
THE MUPPET SHOW.
I can also tell you my least favorite: Big Bang Theory. Ugh. Mute.
Speaking of Deadwood, it also is one of my favorite opening sequences:
Other best credits: Carnivale
American Horror Story
Six Feet Under
Flight of the Conchords
Hmmm. What else? Simpsons and their many variations. Dead like me? Bored to Death? Game of Thrones? Angels in America? Borgias? The Pacific? United States of Tara?