LOONEY TUNES (I suppose the avater is a bit of a giveaway). Although, you know, not so much from MY childhood as my grandma's, BUT I STILL WATCHED IT SO IT COUNTS. Teen Titans was a lot of fun, I'll have to hit it again for nostalgia's sake. And Avatar, dear god, that's still good, even though by the time I accidentally stumbled across it I wasn't so much a kid anymore. As for Xiaolin Showdown, I dunno, I remember watching it, I remember enjoying it, but I think I sort of quit after a while, it lost its interest. Also some obscure Hanna-Barbera Stuff.
I sort of didn't have cable TV at my home (had it at my grandparents when I was over) until I was 9, so I missed a lot of stuff. My best friend LOVED Reboot, I never saw any of it.