Davey Boy Smith and Regal would have been a great British Bulldogs type team, as heels they would have been a major tag team draw around 1996/98 WWF, I think better than the Bulldog/Owen or Owen/Yoko teams.
Ricky Steamboat and The Rock would have been something to see if Ricky had been fit enough and still active, though I think Steamboat and Steve Blackman could also have been a really good team...
I think Rick Rude and Steve Austin did do a bit of teaming during the Dangerous Alliance days, they would have been a great heel combo for WCW or WWE in the 1994 days had Rude been fit, especially with Paul E or Heenan as the mouthpiece.
Mr. Perfect and Ric Flair - This was the team that should have really happened in the WWF in 1992/1993... Flair didn't want to work tags as he felt it was "beneath him" ... But he and Perfect could have really done some great work as a team, particularly when the Steiners came in shortly afterwards... That was a major missed opportunity for the WWE... Curt never got over as a face and soon jumped...
The Patriot and The British Bulldog - Davey Boy was so good in tags, he could work with pretty much anyone except Lex Luger... The Allied Powers was an ok concept, let down by Lugers shockingly bad face persona... The ideal, Del Wilkes in the WWF 2 years earlier as The Patriot... They would have been a good power based team, and worked far better with the poor mix of teams like the Blu's and the Godwinns...
Bam Bam Bigelow and Jerry Lawler - They did this a couple of times on RAW back in the day, but I always thought Bigelow would have made it bigger with a proper mouthpiece, not Luna... I think a team with Lawler calling the shots and using Bigelow in the Enforcer role would have really worked... They would have been more interesting than many of the teams around in the poor Corporation days.
Brian Pillman and Owen Hart - WWF should have made the earth move to sign Pillman after the Hollywood Blondes reign... Once the Hogan Era began, he would have been a great steal and teamed with Owen you would have had 2 great heel mic workers, with High Flying exciting matches... It would have been World's Greatest Tag Team but 10 years earlier...
Kerry Von Erich and Barry Windham- In the early 1990's after Kerry's IC reign ended, this team would have filled the Void left by the Rockers, Harts and Demoliton all splitting up... they could have feuded with Money Inc over the tag gold far more effectively than the Natural Disasters did...
1980's wise, I think the WWF really missed the boat by not putting Jake Roberts and Ricky Steamboat together... they would have been a really exciting team for the time around Wrestlemania 4...
I also think that the WWF should have brought Hall and Hennig over together as a team...