Everyone should already know about Dexter's Laboratory. It's that simple. This show was one of two shows I remember taping when I was a kid, and I regretted not taping more for a long time. Recently I've gotten access to the show and it holds up tremendously. Dexter's Lab gave rise to superstars in the animation world like Genndy Tartovsky (the show creator), Craig McCracken and Seth MacFarlane.
The show itself had a great 1950's tone which was in no small part due to the art style. The simple and clean lines were matched perfectly with an colourful yet slightly muted colour palette. This art style and tone were heavily carried over into the Powerpuff Girls when Craig McCracken started that project.
In terms of writing, Dexter's lab had a very unique feel as all of the episodes were made up of 8 minute shorts. This gave the show the advantage of incorporating other segments such as The Justice Friends, Dial M for Monkey!, and my favourite one-off short dedicated to my doppleganger Mandark (according to my wife). It's easy to see where Dexter's Lab's influences were from (like comic books and kaiju), and how they bled all over the show. I can't stress how much I loved this cartoon.