A Game of Thrones. I can't believe they're cancelling it already. After TWO episodes, are you kidding?! It looked so good too, I was really into it.
/horrible trolling attempt...
OP, I totally remember that Starship Troopers cartoon, I used to love it back in the day. It reminds me, though, of another show that I cant remember the name of... Maybe you other children of the 90s can help me out here... It was an animated GI-Joe-ish kind of show about this team that goes around hunting aliens... It was something like... 'B.A.D.: Bureau of Alien Detectives'...
Anyways, I'll have to agree that the all-time greatest prematurely canceled show is Firefly.