Trap door (technically animation, but still amazing..."Burt!")
Stopit and Tidyup
The old Hulk cartoons ("This is Stan Lee, giving you another episode...")
Transformers
Samurai Jack
Speedy Gonzales
The list just goes on and on. As for a favorite? It would have to be either Megatron (Transfromers) or Boney (Trap Door).
Of cartoons from the USA: Batman (Dark Knight and the newer, shinier Batman Beyond version). I really dig Catwoman, but her cartoon versions have just been lacking.
Of the cartoons from abroad (namely, Japan): Kogepan generally ties with whatever flavor of the month has my attention, which I suppose makes him first by default?