What's The Best Season (Not Series) Finale Of All Time?

It's hard enough to end a TV show with grace and beauty — but it's even harder sometimes to craft a season finale that wraps up a ton of storylines in a wonderful, satisfying way — knowing you have to come back the next year. Including a cliffhanger sometimes! What's the best season finale of any SF or fantasy show?

Please include a clip or picture for your chosen season finale. And please mention the name of the show, the name of the episode, and why it was so great. Thanks!

Top image: Buffy the Vampire Slayer, "The Gift." Amazing conclusion to the season-long arc, a great summing up of where Buffy had arrived at, and a fantastic cliffhanger.