The FG to beat SD and make the playoffs for the first time in Arizona was huge, and so was Plummer's TD pass to Sanders.
Hightower's TD against the Eagles wins logically because we know they didn't win the next game--so it was this play that actually took us to our highest level as fans (well, except for fans from 1947).
Larry's go-ahead TD in the Super Bowl was probably the greatest play in a vacuum. Never have I been more excited as a sports fan.
But in a way, the play to beat Green Bay in overtime was the greatest, not only because it capped off one of the most entertaining playoff games ever (possible featuring two HoF QBs), but because it finally felt like we were cheering for a REAL team, and that the Super Bowl year wasn't just a Cinderella story.