Dora, Diego, Sesame Street, Sprout, Noggin, Clubhouse Disney, Blue's Clues, Barney... seriously. These programs my daughter has been watching often since she was 1.5 years old. Most of the time, I'd watch with her and play along with her when the characters would be teaching, etc. It also helps with socializing, how to treat others, how to listen to adults, etc.
My daughter went into kindergarten 2 weeks before she turned 5 y/o and was only accepted because of her emotional maturity and love of learning. She's now one of the top academics in her private school kindergarten class.
TV is only bad when you don't use appropriate programs, use it as a babysitter most of the time, or allow your child to make the TV rules. For those who make the right choices with TV, their children get a huge boost.