Warrior's at Mania 8 was awesome
My favorite though was on Raw in 97 when Pillman jumped out of the crowd and assulted Austin, getting some payback on him
I also liked Owen Hart's when he returned and attacked Shawn at the DX PPV.
HHH's return on Raw in 98 when he saved X-pac from losing his European Title. He had been injured for a bit.
There was another good one around 2000 on Raw when Paul Bearer and Kane returned in a big 10 man tag match between DX/Radicals vs the babyfaces. Remember Paul Bearer steps out and the place loses it.
nWo's was great as well as HBK's return to join the nWo
Another shocking one in 95 was Luger's return to WCW on Nitro.
The biggest though? Come on. Hogan's return to WCW in 96 at Bash at the Beach