I wasn't around when JONNY QUEST was first on the air, but my older sister used to rave about it. It was only a couple of years ago that I gave it a shot and man was she right.
This Hanna Barbera Cartoon from 1964 (ignore all of the other incarnations) is outstanding both in story and art-- with designs by Alex Toth and Doug Wildley this is a cartoon for people who think cartoons can only be for kids.
I think it's the blacks used in the cels that really make it pop. This ain't no Scooby Doo or Huckleberry Hound (and I'm fans of both) but an exciting and dramatic action adventure show which inspired the great VENTURE BROS cartoon that runs on CN now.
All 26 episodes are available through Amazon.