Season 6 finale of Stargate SG-1 works amazingly well.
Breaking Bad Season 5.0 finale would have worked.
Heroes should have blown up NYC, that would have been amazing. And each season should have been like American Horror Story but with different actors and maybe a tiny bit of crossover.
Farscape season 4 ending I almost like more than the miniseries ending.
The ending of season 2 of BSG is the real ending to me.