Thank you, Todd, for jogging my memory about Johnny Dankworth's cool jazz theme which is often overshadowed by Laurie Johnson's better known theme (which I also like). While not as memorable, Johnson also used the beginning of his 60s theme music for "The New Avengers" in the mid-1970s.
Jeff Willis, you have such a great list of classic TV themes that it's hard to add much to it, but I'm partial to Nelson Riddle's work and would add, at a minimum, the themes from "Route 66" and "Emergency!" to the list. I'm also somewhat surprised that no has yet mentioned one of the most...