The episode whose music makes the biggest
impression on me is "The Conspirators".
We see Columbo driving around Los Angeles
with Irish music in the background!
It really sets the mood.
Another series where the music is absolutely
vital is Mission Impossible. This is a show
with very little action (just like Columbo).
For example, there are scenes where all
we are seeing is Barney connecting some
wires. The music's job is to build up
the tension, communicating to the viewer
that this is important and you should
pay attention to what is happening.

I agree. The musical scores are inspiring and conjure-up instant flashbacks to certain scenes -- even when they're re-used in different episodes.