1.22 "Devil's Trap"
I don't think a season finale has ever compared to what the the first season did in terms of cliffhanger endings. Although I wasn't involved with the show during this time, I remember people talking about it, about how they couldn't end it like that, that the show had to be picked up for another season to make sure everyone was okay. It definitely gave people something to talk about. Also, in terms of story, it fit with the theme of the first season, of the familial bond between the brothers and their father, of saving their father, of being a family again.
Runner up: 2.22 "All Hell Breaks Loose, Part 2" since it gave a full-circle ending to everything we dealt with over the first two seasons, with avenging their mother's death (and for Sam, avenging Jessica's death). I consider S1 and S2 to be connected together with giving that closure to that aspect of the story.
Rest of the 30 Days of Supernatural Challenge.
Can I just say that I am loving fandom right now? The cracky gifs, the discussions of the meta episode, theorizing the alternate universe, and right now I am having Dean/Misha, Dean/Castiel/Balthazar and Misha/BAMF!Castiel plotbunnies in my head. EVERYTHING IS BEAUTIFUL AND NOTHING HURTS. ♥
There's no new episode next Friday, right? Or for the rest of the month since it'll be March Madness?