I always liked the Everwood theme for an instrumental, as well as the themes for the 1985 Anne of Green Gables and it’s spinoff Road to Avonlea.
For themes with words, I always find myself singing along to the original One Day at a Time theme song, as well as the Love Boat theme. I don’t think many shows have the type of big theme song these days like they used to. Big Bang Theory was one of the last ones I enjoyed.
It seems like a lot of shows now go for a hook, a two to three measure theme song, and right into the show. I assume it’s to maximize show time as the minutes taken by advertising continue to grow.