This could be a long post, I've got a lot of time to kill and an going to attempt to nail all the big ones and why:
Gotch vs Hackenschmidt I- Helped cement Pro Wrestling as a major entertainment force in the US moving it away from it's carnival sideshow roots, as well as the unification of what is generally considered the first wildly recognized World Heavyweight Championship.
Gotch vs Hackenschmidt II- Wildly accepted as the first major predetermined wrestling match as well as one of the first known screwjobs. While there had been predetermined matches before, they were always at a small carnival level, not a national event like this was.
Sanislaus Zbysko vs Wayne Munn- led to be the beginning of widespread speculation of wrestling's legitimacy as competition.
"Gorgeous" George Wagner vs "Whipper" Billy Watson- Generally remembered as the pinnacle of the TV Era and was one of the most viewed events in televisions then short history.
Lou Thesz vs Nature Boy Buddy Rogers- As has been said, led to the split between Capitol Wrestling Corporation and the NWA. CWC would quickly be named WWWF and the rest is history.
I've run into a bit of a problem now, as I'm not as knowledgeable with the 60's and 70's as I am before and after, plus because wrestling was in a downturn in popularity during this time I'm having a really hard time coming up with historically significant matches so any help here would be appreciated!!
Hulk Hogan vs The Iron Sheik- While not the match that started the Rock n Wrestling boom it's the one to start the ball rolling and establish Hogan as the face of not only the WWF but professional wrestling. Less then a year later and Hulk Hogan would be a household name.
Wendi Richter vs Fabulous Moolah- The Brawl To Settle Them All. This is the match that kicked Rock n Wrestling into high gear as millions of people tuned into see Richter, accompanied by Cyndi Lauper, defeat Fabulous Moolah putting an end to what was being billed as a 28 year Women's Title Reign. MTV scored a 9.0 rating, it's highest ever in it's short existence
Roddy Piper vs Hulk Hogan- The War To Settle The Score. This match set up the WrestleMania mainevent and led to another monster rating for MTV, at a 9.1. The match is easy to overlook, but without it WrestleMania very possibly could have failed.
Hulk Hogan and Mr T vs Roddy Piper and Paul Orndorff/
Lelani Kai vs Wendi Richter- I lumped these 2 together because I consider them equally important. While WWE now glosses it over, but just as many people watched Wrestlemania because of Richter and Cyndi Lauper as for Hogan and Mr T. If this event failed, the WWF would have failed with it.
Hulk Hogan vs Andre The Giant- The big one, 93 000 fans in attendance and millions around the world watched Hogan slam Andre in what is likely the most famous wrestling match of all time.
Hulk Hogan vs Andre the Giant II- The Main Event, over 33 million people tuned in to witness the end of Hulk Hogan's legendary title reign. The most watched match in wrestling history a number that will likely never be replicated
Hulk Hogan vs Ultimate Warrior- To me, this is the end of the 2nd Golden Age of Wrestling. While Hogan would be around for another 3 years, this is the first of numerous to replace him and the end of the Hulkamania era.
The Outsider's and Hogan vs Savage, Luger, and Sting: The formation of the nWo the most important and well known faction ever in wrestling and the beginning of the 3rd Wrestling Boom. Also, a major factor in intensifying the Monday Night Wars
HBK vs Hart- The Montreal Screwjob. One of the most know, and debated matches ever. While the match itself is not that important, the fallout led to the resurgence of the WWF in the Monday Night War and most importantly kicked off the Attitude Era.
Sting vs Hulk Hogan- The match over a year in the making got WCW it's highest PPV buyrate ever, but this match is more remember as a disaster that was the beginning of the end for WCW. 3 short years later they'd be gone....
HBK vs Stone Cold- Everyone was talking about when Mike Tyson showed up on Raw, and millions paid to see him as the Special Enforcer in this match. Once again, outside factors are more important than the match itself but once again everyone was watching the WWF and they have Stone Cold and Mike Tyson to thank for it.
Austin vs McMahon- An easy one to overlook, but Austin vs McMahon's first match was the WWF's first ratings victory in almost 2 years since the formation of the nWo. While they battled with WCW for a while longer, the WWF scored a major victory here and finally started winning battles in the MNW
Austin vs The Rock II- The 2nd of 3 WrestleMania matches between the 2 Icons of the Attitude Era is memorable for signifying the end of an era for the WWF. Much like Hogan/Warrior 11 years prior, this marks the end of widespread mainstream popularity of wrestling.
Booker T vs Buff Bagwell- While the match is best remember as a complete disaster and basically ruining the WCW name in the WWF's eyes, the fact is that it was the first time the WCW Title was defended in a WCW match on WWF Raw. Most people try to forget this match due to it's terrible quality, it does hold a place in history for the simple fact that this was a simply mindblowing idea, and every wrestling fans wet dream only 2 years prior. But, the whole handling of WCW ended up leaving a bad taste in everyone's mouth.
Chris Jericho vs Steve Austin- While events since have erased this from being nearly as big of a deal as it should be remembered, the WCW and WWF World Title Unification match would the first time WWF would be able to lay claim to having the Undisputed Champion atleast as far as North America goes, and the first one in North America in close to 50 years.
I think that about covers the bases, atleast for the time being. I know it was a very long winded post (longest I've ever done I think) but hopefully ya made it through. So now, I might as well open it up to what people think should be added or subtracted especially those with about knowledge of the 60's and 70's. This is very WWF heavy so I imagine I missed some NWA/WCW as well as others so feel free to toss some out