The one that I never thought could be topped was the game in DC several years ago when we were lined up to kick the game winning FG. But not only was it blocked, but run back to mid-field and then a personal foul penalty set the Redskins up for the winning FG as time expired. I think it was in '08 or so because TO was still playing for us.
IIRC, score was tied and Romo-to-Witten long completion magically got us into FG position for the last play of the game.
1. Witten misses block.
2. A Redskin blocks Vanderjagt's FG attempt
3. Time has expired - if play ends, it's OT
4. Sean Taylor picks up the ball and runs about 15 yards.
5. A Cowboy facemasks Sean Taylor, so 15 yard penalty more.
6. With 00:00 on the clock, one more play is granted for the penalty.
7. Ex-Cowboy cut that training camp, Nick Novak, kicks a GW ~50 yard FG.
It doesn't get any better than that.