My first choice would be Samurai Jack. After reflecting on my child hood, I can safely say that that was my favorite cartoon. And my inner child needs to see Jack run his sword through Aku one final time.
And Firefly, because it's completely unfinished, even with the movie.
Also I'm sick of you people thinking they don't run the episodes anymore, Early in the morning, Maybe 7 to 9 they show the reruns of all those shows. The cartoon network ones anyway.
Reruns don't count. You can get reruns on the internet anyday.
