Hard to argue any of the plays mentioned in this thread.
For me:
1) Beast Quake - For some unfathomable reason the wife and I forfeited our playoff ticket seeding that year (must have been our record) so it was purely luck that I was able to still go to the game thanks to one of my best friends. He had two tickets in the upper level. I remember that moment like it was literally yesterday. I've seen nearly every single game in the "new" stadium (Seahawks Stadium/Qwest/Century Link) since it opened in 2002. I've seen some epic, historic moments and games no doubt. But that one moment, when Lynch broke out the most spectacular run in NFL history (it's not even debatable to me) I simply new in that moment, that my beloved Seahawks had arrived. They were finally lifted from the back of the pack to a team to take quite seriously. Oh, and yes, I really did think the stadium was going to collapse and I would have loved knowing that's how I went out.
2) The Tip - I've had a ton of games that made me nervous, but NO game I have ever attended at home made me feel as nervous as this one going into it. I remember as we drove on I-90 heading towards the stadium that day telling my wife "I feel sick, like the kind of nerves you feel going into a major job interview". I couldn't help it. I couldn't shake it. My hatred for the 49ers was so severe at that time it nearly crippled me. The very thought of that team...THAT coach...THAT quarterback going to the Super Bowl in our house was just too much to bare. The game of course as we know was an instant classic. It looked grim for a while and then in that historic moment when Kaep drew back and launched that pass into the endzone (OUR endzone...That was the corner endzone we were standing in just 50 yards up) my wife turned around and said "I can't! I can't watch!!" A split second later, when the world around us erupted in pure ecstacy....Man...Those are the reasons you suffer and pay those prices every year.
3) Super Pick 6 - I know a lot of you think the Harvin kickoff return TD was one of the best plays and I certainly cannot argue that based on what that play meant, but for me, it was the Smith pick of Manning in SBXLVIII which gave me that feeling that, "Oh, it's over. We are Super Bowl Champions!!!" Yes it was earlier in the game but intuitively I KNEW in that moment the game was over. at that point, the Harvin TD was nothing more than icing on the cake.