Well, there's Detention, Cybersix, Megas XLR, Clerks, Invader Zim and Mission Hill.
I always felt that those shows deserve a second season. And what bothers me is that despite any sort of praise some shows although Detention had mixed reactions, the networks just don't bother to renew them.
I guess they didn't bring them back probably because of ratings, delays, etc. You know?