And from the original article:
"some other notable showkillers include Blair Underwood, Krista Allen,
Aidan Quinn, and Donnie Wahlberg."
Conspicuously missing from the list thus far: Summer Glau!
http://www.complexmag.ca/pop-culture/2012/11/25-best-season-finales-of-all-time/
also has a glaring omission: Star Trek TNG's "The Best of Both Worlds, Part
1". The DS9 season 5 finale "Call to Arms" probably also deserves mention.