For starters, just about all of his WrestleMania singles matches.
Wrestlemania IX - Shawn Michaels and Tatanka put on practically the only good match of the event (and likely the best match of Tatanka's career).
Wrestlemania X - This show is famous for Shawn's ladder match against Razor Ramon, which had a few Crowning Moments of its own and is probably the highlight of Scott Hall's WWE career. PWI's Match of the Year.
Wrestlemania XI - Shawn started his face turn with a match that's probably the best one Diesel's ever been a part of. Match of the Year.
Wrestlemania XII - Shawn and Bret Hart put on a stellar Iron Man match that lasted for over an hour; both men listed this as a top contender for best match of their respective careers, even throughout all of the acrimony that followed thanks to the Montreal Screwjob. This match is also significant for being Michaels' first major title win. Match of the Year.
Wrestleman XIV - Shawn competed with a severely injured back, put on an absolutely legendary match, and put Stone Cold over as a world champion; in the process, he helped launch the most successful period in WWE history.
Wrestlemania XIX - After missing four WrestleManias thanks to that injured back, Shawn made his return and defeated spiritual successor Chris Jericho in what many consider to be the show's best match. "Match of the Night" may not sound all that impressive, but keep in mind that this particular night also featured the final WrestleMania match between Rock and AustinandBrock Lesnar vs. Kurt Angle.
Wrestlemania XX - Shawn puts on a clinic in a Triple Threat match with Triple H and Chris Benoit. This would be Michaels' fourth PWI Match of the Year match at a WrestleMania (and his fifth overall). To put this in perspective: at this point in time, nobody else had been in more than four Matches of the Year in their entire career, never mind at one specific event.
Wrestlemania XXI - Shawn Michaels vs. Kurt Angle. Match of the Year. This is what happens when you put two guys who are used to/capable of putting on **** matches with total scrubs in the ring together.
Both of their rematches were of comparable quality, as well.
Wrestlemania XXII - Shawn beats the tar out of non-wrestler Vince McMahon and still somehow puts on a good enough show to rake in another Match of the Year.
Wrestlemania XXIII - Shawn Michaels vs. John Cena. Largely considered to be one of the top five matches of Cena's career, this one sadly did not win Match of the Year (although their rematch later that month did). For those of you keeping track at home: at this point, Michaels had won four consecutive Matches of the Year, as many as anyone else had managed in their entire career.
Wrestlemania XXIV - Shawn retired wrestling legend Ric Flair in another epic, which gave Michaels his fifth consecutive Match of the Year award, sixth at WrestleMania, and ninth overall, more than double the number of any other wrestler - except Ric Flair, who picked up his fifth in this match. The last time Flair had won the honor prior to this match was in 1989.
Wrestlemania XXV - Shawn went up against The Undertaker, absolutely stole the show, and snagged his tenth Match of the Year (sixth consecutive, seventh at WrestleMania).
Wrestlemania XXVI - In the final match of his career (for now), Shawn headlined the "Showcase of the Immortals" one last time in a "Streak vs. Career" rematch with The Undertaker. After kicking out of TWO Tombstone Piledrivers, a Last Ride, and Taker's annual over-the-top-rope plancha, Michaels finally went down to a jumping Tombstone Piledriver. His reward? A mind-blowing eleventh PWI Match of the Year, ending his streak (barring a surprise comeback) at seven. The second longest streak? Four, from 1993-1996, held by...Shawn Michaels. There's a reason they call him Mr. WrestleMania.
Put it all in perspective: from 1993-2010, only seven matches were awarded Match of the Year that WASN'T a Shawn Micheals match, three of which he didn't even wrestle at all during that year and two of which he was gone for most of the year due to his forced retirement. Even with a four-and-a-half absence in the middle, HBK dominated two decades of Match of the Year.
Along with PWI's Match of the Year awards, Shawn also won the Slammy for Match of the Year every year that WWE held them when he was active: 1996 (the Ladder Match against Razor), 1997 (the Iron Man Match against Bret), 2008 (the hour-long match vs. Cena in England), 2009 (Shawn/Taker I), and 2010 (Shawn/Taker II). All of these matches, save for the 2008 match, were WrestleMania matches.
In short: the nickname "Mr. WrestleMania" isn't just for show.
Beyond his many WrestleMania accolades, Michaels was pretty much the guy who validated new match formats. He was involved in WWE's first ladder match (losing to Bret Hart), the first Hell in a Cell match (he defeated The Undertaker), the first Iron Man Match in WWE (he defeated Bret Hart), and the first Elimination Chamber Match (where he defeated Rob Van Dam, Booker T, Chris Jericho, Kane, and Triple H). All four of those formats have gone on to be popular in WWE (and in the case of Ladder and Iron Man Matches, the industry as a whole). All four are still generally associated with Michaels (who competed in each one at least twice).
A specific match that deserves some attention is his Survivor Series 2003 match. With Steve Austin's career on the line in a Survivor Series Match, it comes down to Shawn Michaels facing off with Christian, Randy Orton, and Jericho. Beaten and bloodied, he manages to take out Christian, then Jericho, and has Orton beat before interference from Eric Bischoff and Batista ultimately costs him the match. To top it off, he and Austin - old rivals who put on two absolutely classic matches themselves - share a powerful moment in the ring that is more or less painted with Shawn's blood by this point. Oh, and he goes and avenges the loss by beating Batista about a month or so later.
Did the above troper just imply that The Undertaker needs to have a good match dragged out of him?
Lately? Yes.
Four words: "Who'syour daddy,Montreal?!" Easily one of the best promos he's ever done, and even more brilliant considering that one was delivered AFTER he got religion and cleaned up his life, proving he could still be one of the best heels in the business. Watch all 16 minutes of brilliance here.
Being the first man ever to win the Royal Rumble from the #1 spot, outlasting 29 other wrestlers.
The "Let There Be Light" promo he did before WrestleMania 25. Hell, all the promos he did leading up to that qualify.
His comeback match with Triple H at SummerSlam 2002. No one thought Shawn, four years out of the business, after a crippling back injury, would have a chance in hell against Triple H in his prime. No one expected it to get that hardcore. No one expected Shawn to last 4 minutes, never mind forty-five - or to actually win.
Shawn and Hunter's hellacious 50-minute Last Man Standing match at Royal Rumble 2004, which was capped by a no-contest finish in Philadelphia and made the Mutants give both men a standing ovation.
The aforementioned Match of the Year winner that wasn't at Wrestlemania: his rematch with John Cena on Raw. Cena and Michaels went a solid fifty-nine minutes (they were originally supposed to have a much shorter match, but backstage reasons forced them to fill time) and put on a Pay-Per-View-worthy wrestling clinic for free on television.