The Stinger for WrestleMania IX featured Kamala "communing with the animals" backstage at Circus Maximus. He was supposed to fight Bam Bam Bigelow, but the match didn't happen due to to time constraints.
The footage of OJ Simpson being pursued by police getting reused in the Hollywood back lot brawl between Rowdy Roddy Piper and Goldust at Wrestlemania 12.
Made even funnier with Vince McMahon and Jerry Lawler hanging lampshades over the use of the footage. Vince even remarks "You know I have to say that this footage looks...awfully familiar."
The commercials for WrestleMania 21, such as Triple H parodying Braveheart and Ric Flair coming in with a mule. Other examples include:
Undertaker doing the famous "Did I fire six shots, or was it only five?" ending with the signature eye roll.
Christy Hemme and Kurt Angle do the famous scene from "When Harry Met Sally", complete with Kurt wearing a ridiculous wig.
Linda McMahon: I'll have what she's having.
Various superstars doing the "You talking to me?" line from Taxi, ranging from Big Show unable to do it, and Batista with a Who's on First? routine.
Basic Instinct with the three Chris's (Chris Jericho, Chris Benoit and Christian) interrogating Stacy Helms engaging in different "activities". Including this famous line:
Christian: How about sadomasochistic activity?
(cue Chris Jericho and Benoit staring at Christian)
Christian: Just asking.
Eugene as Forrest Gump, ending with William Regal screaming, "Run Eugene, run!" after Eugene accidentally punches the old woman on the bench out.
Eddie Guerrero and Booker T as Vincent Vega and Jules Winnfield and Booker T doing his own version of Ezekiel 25:17, ending with Booker T patting Eddie on the back for an I Just Shot Marvin in the Face gag.
Hardcore Championship madness at WM18. The title changed hands from Maven, Spike Dudley, The Hurricane, Mighty Molly, Christian and back to Maven.
Boogeyman vs Booker T at WrestleMania 22, both the build up and the actual match.