Bud Collyer also did Superman's voice in the 1941 Fleischer cartoons and in the 1966 "The New Adventures of Superman", if you want to include his other works. And if we're talking quality of animation, I think the Fleischer series must be included.
Superman Homepage says Michael Fitzmaurice did Superman's voice in the final season of the radio show.
IMDB lists Danny Dark as Superman's voice actor in the Super Friends series'. I seem to recall it as having been popular - at least, I think it was the show re-running in the mid-to-late 80s when I was growing up.
I'd consider the Animated Series (1996) with Tim Daly and Justice League (IMDB lists George Newbern) as significant enough to mention.
When it comes to all the movies, I have no clue what/who significant enough to count.
