Only one choice?
Well, I would vote Batman Beyond, but I actually watched that on Toonami.
When I was younger, I pretty much watched anything on Fox, WB, Disney, or Cartoon Network (there was another channel I can't remember too)
I caught things like Beast Wars, Transformers, Tiny Toons, Freakazoid, Pinky and the Brain, Animaniacs, Static Shock (mostly the cartoon network afternoon run, though), some scooby doo show, some hamtaro, Pelswick, and various other cartoons like Ed Edd and Eddy, Hey Arnold, Jimmy Neutron, Catdog, Kablam, (Basically the nicktoons show).
No Power Rangers, though, I wasn't allowed to watch that. My parents couldn't keep me from watching DBZ, though. They were pretty laid back, just no Power Rangers, I could watch anything else though, my dad even let me watch Ghost in the Shell (He thought it looked interesting). My Brother ended up watching Tenacious D at a young age, though; my mom didn't know it had so many F-bombs, but once it started, she went ahead and watched it with him.