I also loved those Irwin Allen opening titles. The Williams stuff were arguably better when he had the second run at them. Lost in Space' first and second season themes (really the same recording) were a little silly and one could be forgiven for thinking the series was a comedy when it first started (the series grew into the theme as it went along). The third season's theme was a huge improvement and really upped the ante in excitement. I wasn't as fond of The Time Tunnel, it was a bit "on the nose" with the tick-tocking. But if it went to a second season, I imagine Irwin would have had Williams back to redo it because that's what he did. Land of the Giants: LOVE the second season theme, and it's among William's best TV themes.
Voyage to the Bottom of the Sea always had great theme music. Paul Sawtell's lilting seafaring composition is just marvelous. Jerry Goldsmith was hired to provide a new theme for the second year, and it was used only once in the premiere (along with his outstanding background score) before the more appropriate Sawtell theme was restored. I like Jerry's theme a lot, but it's a little too downbeat for such an adventure show. The DVDs incorrectly put the Goldsmith end titles on the following episode as well.
Other fantastic 60's TV themes include:
The Outer Limits
The Rat Patrol
The Wild, Wild West
The Invaders
I Dream of Jeannie (both the Wess and Montenegro versions)
I Spy
The Avengers (Laurie Johnson's stuff)
Doctor Who
and from those great ITC series:
The Saint
Man in a Suitcase
The Champions
Department S