Any Tex Avery cartoon (esp. Droopy)
Battle of the Planets (loved the series as a kid)
South Park
Simpsons (at their peak - to me they have definitely gone off the boil)
Futurama (loved the episode with the intelligent chimp, but need to watch it more often)
Ren & Stimpy
Samurai Jack
Justice League (I can't get into JL Unlimited, though)
Batman of the future (an intelligent twist to a comic legend - unlike Marvel's crap "2099" comic line)
Tin-Tin (loved it as a kid)
oh yes...early Tom & Jerry (the later cartoons looked crap and were crap)
Would have added Wacky Races - if only they'd left Dick Dastardly & Muttley win a few - it got a bit boring seeing them get their come-uppance each week...