My list is fairly short, but here goes. Keep in mind, all Stars would of course be in their Primes.
Hulk Hogan vs. Stone Cold Steve Austin
This would be the real Icon vs. Icon Match of the Century. I still believe it should have been these two at WM X8 with Rock teaming with Undertaker to face the Outsiders instead. To me, it would have made more sense.
Outsiders (Hall and Nash) vs. D-Generation X (HBK and HHH) with 1-2-3-6-X-Pac as the Special Guest Referee
Clique vs. Kliq. I would have loved to have seen this match with the history of these 5 men. I feel they were the greatest Stable to never exist.
Four Horsemen (Flair, Anderson, Blanchard, and Windham w/Dillon / Flair, Benoit, Malenko, Mongo w/Anderson) vs. New World Order (Hogan, Nash, Hall, Giant w/ DiBiase) vs. DX Army (HHH, Pac, Road Dogg, Bad @$$ w/ Chyna) with HBK as the Special Guest Referee
The Dream Match part would be the Windham Era, all in their primes, but the Reality Match part is, of course, the Mongo Era. This Survivor Series / War Games Match should have happened along with the Main Event of McMahon vs. Bischoff, if they could have ever agreed to it.
The rest of these are just Dream Inter Promotional / Inter Era (if thats a word) Matches, just to throw it out there.
Hulk / Ultimate Warrior vs. Sting / Lex Luger
The Top Two Stars in WWF in 1990 vs. the Top Two Stars in WCW in 1990. This match could have actually started a second Civil War among Wrestling fans in 90. Classic North vs. South. I dont think Cena and Triple H (or HBK) vs. Undertaker and Jeff Hardy (I picked Jeff, only because of his Extreme popularity, or I would have picked someone on the current roster, like Batista or Mysterio) vs. Styles and Sting in a Triple Threat Tag Team match could even be bigger than this.
And on the other side of that coin
Mega Powers vs. Ric Flair and Sting
The Top Face and Heel in WWF in 1989 vs. the Top Face and Heel in WCW in 1989. This match could have actually started a second Civil War among Wrestling fans in 89. Classic North vs. South, rivals putting their huge differences aside for the good of their respective companies. I dont think Cena and Orton vs. Undertaker and Punk vs. Styles and Angle in a Triple Threat Tag Team match could even be bigger than this.
Stone Cold Steve Austin vs. Goldberg
This was the Attitude Eras Hogan vs. Lugar or Warrior vs. Sting. Sort of similar appearances and superstardom, yet two completely different types of characters. At the time of the Undefeated Streak, I remember constantly saying, If anyone can break it, Stone Cold can!!.
Andre the Giant vs. Big Show
Theres nothing I can really say about this, but I just want to see it. Ive actually made them a Tag Team in Legends Of WrestleMania as the Giant Show.
Hurricane, Kane, and Rosey vs. the Prince Justice Brotherhood
Its Marvel vs. DC. Actually, maybe it would have been more entertaining to put them all in one Stable called
World Elite (play on Worlds Finest)!!
Bob Orton, Dusty Rhodes, Ted DiBiase w/ Vince vs. Legacy w/ Shane
Who hasnt thought of this?? Fathers vs. Sons always make great Storylines.
Brothers of Destruction vs. Fake Undertaker and Fake Kane
I just think this would be cool to see. Maybe change it up to two Takers vs. two Kanes or Real Taker and Fake Kane vs. Real Kane and Fake Taker.
Triple H vs. Brock Lesnar
The Championship Match that never happened. What was the problem anyway?? Whatever the case is, I think this match should have either happened at Unforgiven 2002 or WrestleMania XIX, right after the WWE Title Match (if Botch Lesnar didnt do his Falling Star Press, of course, and could continue)
I could keep going.