Buffy The Vampire Slayer

Buffy the Vampire Slayer, "The Gift"

Buffy season six probably isn’t most people’s favorite season — but at least the cliffhanger of "Buffy sacrifices her life to save the world" is resolved in a suitably epic way. Buffy’s friends go to great lengths to bring her back from the dead, and there are clearly huge costs to this choice, which play out over the entire season.

(...)

Click on the link for more :

http://io9.com/5919649/season+ending-tv-cliffhangers-that-actually-paid-off