1) Firefly as short as it was
2) Battlestar Galactica
3) Fringe
4) X files
5) SG1


Honorable mentions: Game of Thrones, Stargate Atlantis, Deap Space 9, Falling skies, Doctor Who seasons 5 & 6, Bybelon 5

and those who are not with us anymore: V, Flashfoward and Defying Gravity