I'm laughing at all the people saying that Cena/Punk was anywhere close to one of the best ever. It had an awesome crowd and a good angle, but that was it. The match was pretty sloppy in the ring.
For me, its Austin/Rock from WM 17. It seems like kind of a routine answer considering that several people have mentioned it already, but seriously, that match had everything that I as a wrestling fan wanted in a wrestling match. It had the incredible build up before hand, the emotion, the intensity, the passion, the psychology, the drama, the storytelling. It was like if Fyodor Dostoyevsky and Charles Dickens got together to write a story. It was two masters of their craft engaging to create a timeless epic. The crowd was into it, the excitement was edge of your seat, you had literally NO idea who was going to win when it came down to the wire, and most of all, I, for one, became emotionally invested. I CARED about who won. I sat there and watched them hit each other with their finishers and kick out at 2 and 9/10 seconds. Then Vince came out and Austin showed the start of his heel turn, and JR sold the situation absolutely PERFECTLY! That, to me, is why its the best main event ever.
Its also an interesting reason as to why today's roster is so bad for the most part. The guys today can't generate a fraction of any of this, and that's why the IWC bitches and complains about the bad crowds and how silent they are. I can't blame the crowds, I blame the product. They are supposed to make the fans care, and they're doing a pretty awful job. They can't provide a good story, generate intensity, emotion or passion and they totally miss the ring psychology. That's why you get main events like Over the Limit 2011 with Miz and Riley decimating Cena, just for him to come back in 30 seconds and win. What the fuck? What story, what intensity, what emotion and passion, what psychology? It was pure crap. You know who can generate all of these things today? Taker and Triple H, and surprise, they fought each other at WM 17 the same night as Austin/Rock. Face it, these guys are a different, more elite breed, and products of a different time period. Good wrestlers and performers are literally a dying breed. They don't make em like they used to.
Honourable mentions-Benoit/Michaels/Hunter at WM 20, HBK and Taker at Bad Blood 97, HBK and Taker and WM 26, Angle and Lesnar from WM 19 (especially considering how badly injured Angle was).