Drawn Together - Not only a show that was cancelled too soon, but also one of those shows that didn't have a bad season. Crude (Princess Fiona and her octo ... you know what, the many deaths caused by Captain Hero) and hilarious (Ling Ling's Engrish, the Spongebob character whose name escapes me at the moment), I'm very happy to hear a movie is coming. The best animated show I've seen on Comedy Central since South Park.
The Powerpuff Girls - I love this show and I'm a 28 year old man. Is that wrong? I like the super hero aspect and how different the personalities are of each character. It can be for kids, but has plenty of material to keep adults happy.
The Fairly Oddparents - I'm a sucker for paradies so this show drew me in right away. The paranoia the parents exhibit (especially Timmy's dad and Mr. Crocker) are flat out hilarious. Like PPG, there's plenty of adult content here to keep parents and adults away from the "it's just for kids" mentality. Plus, you can't go wrong with a show that has Adam West.
Dragonball Z - I could go on and on as to why I love this show so I'll keep it brief and say DBZ is brilliant.
Transformers Generation 1 - The first action cartoon I've ever seen that blew me away. Giant robots transforming into everyday objects and interacting with humans. The look of the show, the special effects, and the voice acting are so memorable to me; I feel like Bruce Wayne watching The Gray Ghost everytime I see it [on DVD or as a Robot Chicken skit].
And a show that I watched fairly recently: Avatar: The Last Airbender. I like the idea of this kid trying to find his way and meeting people on his journey. There's plenty of action and even some humor in case things get really intense. I've only seen a couple of episodes but personally, I like this show a lot more than Naruto.