1. ole anderson's turn on thunderbolt patterson
 
2. the MX-dangerously attacking the MX and jim cornette.

In no particular order....
1. Barry Windham joining the horsemen
2. Nikita's face turn
3. Terry Funk attacking Flair at Wrestle War 89
 
There were many.... not sure that any of these would necessarily qualify as the "greatest ever", but each had it's own significance as well as countless others

Nikita turning good and joining up with Dusty and Windham joining the Horsemen would be the two best for me.  Funk attacked Flair would be third.

Maybe I should have said greatest Feud and not Angle but ohh well. Here is my top 3.
 
1. Horsemen break Dusty's leg after he saves Flair from Russians.
 
2. Barry Windham joins Horsemen.
 
3. Nikita turns face.

I loved the angle when the Horsemen kicked Sting out in Corpus Christi, Texas. Total shock to me but a great Horsemen moment.

One of my faves is when I believe it was rnr express  put a nuce around jim cornettes neck attatched to a cars bumper and drove away as the show ended  and it came on sat night.

Here is waht I can think of right off the top.I base this on standing out in memory, drawing interest in a feud, and most importantly making me want to spend money to see the resolution.
 
- Terry Funk attacks Ric Flair at Wrestle War 89 and turns him babyface setting up their ultra hot feud
 
- Ricky Steamboat returns as Eddie Gilbert's mystery partner to face Ric Flair and Barry Windham in the tag team match at teh old TBS studios
 
- Barry Windham joins the 4 Horsemen
 
- Nikita Koloff turns babyface to team with Duty Rhodes vs Ole Anderson & JJ Dillon in the cage match in Charlotte
 
- Jim Cornette & the Midnight Express attack Baby Doll setting up the America's Team/James Boys vs Midnight Express feud
 
- Dusty and Magnum show up under hoods as the James Brothers and beat the Midnight Express at the TBS studios
 
- Paul E Dangerously and the Original Midnight Express show up in the studio and attack Jim Cornette and the Midnight Express
 
- Ole & Arn Anderson return in November 89 to save Ric Flair from Muta, Buzz Sawyer, and Dragon Master in a wild brawl all over Center Stage
 
- Mgnum TA & Nikita Koloff get into it at the US Title match press conference leading to Magnum getting stripped of the US Title and the Best of 7 Series taking place to fill the title
 
- Horsemen rub Ricky Morton's face in the concrete in Grenville after Morton had pinned Ric Flair in the 6 man elimination tag
 
-  Dusty goes nuts in the

almost everything that happened on World Championship Wrestling.

I REALLY liked when Barry Windham turned on Lex Luger and joined the Horsemen--on so many levels.

Reading this thread really brought up some great memories...  Some memorable mathes, not necessarily feuds or angles, which to me really sold the NWA/WCW as a true "wrestling" company was Barry Windham vs. Bam Bam Bigelow at Starrcade 1988, where you could see the intensity in Barry - screaming "He's mine JJ", as though he were selling a real contest...  It brought passion to the match, and to me was memorable...
 
Also the intensity of Sting vs. Rick Rude in 1991 after Sting was attacked at a Clash of Champions and came back to wrestle anyway...  I miss those days where you were sold on the idea that you were watching a contest, and it wasn't just garbage time...  The wrestling WAS the main attraction...

Vader vs Jack (brutal matches)
 
Horsemen vs Dusty, Road Warriors  
 
Flair vs ???? (Pick a name you won't go wrong)
 
Midnight Express vs Rock n Roll Express (what tag team wrestling is all about)