Just for information, I did pull up the May PPV events, starting with 1995 and listed the marquee matches (of course, what is a marquee match compared to others is up for debate really).
Useless you may say, work systems down I say
1995: In Your House #1 (May 14th) -
WWE Champion Diesel vs. Sycho Sid... Jerry Lawler vs. Bret Hart
1996: In Your House #8: Beware of Dog (May 26th and 28th) -
WWE Champion Shawn Michaels vs. British Bulldog...
Intercontinental Champion Goldust vs. The Undertaker in a Casket Match
1997: In Your House #15: A Cold Day in Hell (May 11th) -
WWE Champion The Undertaker vs. Stone Cold Steve Austin... Ken Shamrock vs. Vader in a No Holds Barred Match
1998: Over the Edge: In Your House (May 31st) -
WWE Champion Stone Cold Steve Austin vs. Dude Love, with Vince McMahon as the Special Guest Referee... Kane vs. Vader in a Mask vs. Mask Match
1999: No Mercy (May 16th) -
WWE Champion Stone Cold Steve Austin vs. The Undertaker vs. Triple H in a Triple Threat Match...
European Champion Shane McMahon vs. X-Pac
1999: Over the Edge (May 23rd) -
WWE Champion Stone Cold Steve Austin vs. The Undertaker, with Vince and Shane McMahon as the Special Guest Referees... The Rock vs. Triple H
2000: InsurreXtion (May 6th) -
WWE Champion The Rock vs. Triple H vs. Shane McMahon in a Triple Threat Match...
European Champion Eddie Guerrero vs. Chris Jericho... Kurt Angle vs. Chris Benoit
2000: Judgment Day (May 21st) -
WWE Champion The Rock vs. Triple H in an Iron Man Match...
Intercontinental Champion Chris Benoit vs. Chris Jericho in a Submissions Match... Road Dogg & X-Pac vs. Dudley Boys in a Tables Match... Big Show vs. Shane McMahon in a Falls Count Anywhere Match
2001: InsurreXtion (May 5th) -
WWE Champion Stone Cold Steve Austin & Triple H vs. The Undertaker in a Handicap Match... Chris Jericho vs. William Regal in a Queen's Cup Match... Chris Benoit vs. Kurt Angle in a Two out of Three Falls Match
2001: Judgment Day (May 20th) -
WWE Champion Stone Cold Steve Austin vs. The Undertaker...
Intercontinental Champion Triple H vs. Kane in a Chain Match... Kurt Angle vs. Chris Benoit in a Two out of Three Falls Match
2002: InsurreXtion (May 4th) - The Undertaker vs. Triple H... Stone Cold Steve Austin vs. Big Show, with Ric Flair as Special Outside Referee
2002: Judgment Day (May 19th) -
Undisputed WWE Champion Hulk Hogan vs. The Undertaker... Triple H vs. Chris Jericho in a Hell in a Cell Match
2003: Judgment Day (May 18th) -
WWE Champion Brock Lesnar vs. Big Show in a Stretcher Match...
World Heavyweight Champion Triple H vs. Kevin Nash... Mr. America vs. Roddy Piper
2004: Judgment Day (May 16th) -
WWE Champion Eddie Guerrero vs. JBL... The Undertaker vs. Booker T...
U.S. Champion John Cena vs. Rene Dupree
2005: Backlash (May 1st) -
World Heavyweight Champion Batista vs. Triple H... Hulk Hogan & Shawn Michaels vs. Muhammad Hassan & Daivari... Edge vs. Chris Benoit in a Last Man Standing Match
2005: Judgment Day (May 22nd) -
WWE Champion John Cena vs. JBL in an "I Quit" Match... Kurt Angle vs. Booker T... Eddie Guerrero vs. Rey Mysterio
2006: Judgment Day (May 21st) -
World Heavyweight Champion Rey Mysterio vs. JBL... Booker T vs. Bobby Lashley in the 2006 King of the Ring Finals... The Undertaker vs. The Great Khali... Kurt Angle vs. Mark Henry
2007: Judgment Day (May 20th) -
WWE Champion John Cena vs. The Great Khali...
World Heavyweight Champion Edge vs. Batista...
ECW World Champion Vince McMahon, Shane McMahon & Umaga vs. Bobby Lashley in a Handicap Match... Randy Orton vs. Shawn Michaels
2008: Judgment Day (May 18th) -
WWE Champion Triple H vs. Randy Orton in a Steel Cage Match... The Undertaker vs. Edge for the vacant
World Heavyweight Championship...
WWE Tag Team Champions John Morrison & The Miz vs. Kane & CM Punk... Shawn Michaels vs. Chris Jericho... John Cena vs. JBL
2009: Judgment Day (May 17th) -
WWE Champion Randy Orton vs. Batista...
World Heavyweight Champion Edge vs. Jeff Hardy...
ECW Champion Christian vs. Jack Swagger... John Cena vs. Big Show
2010: Over the Limit (May 23rd) -
WWE Champion John Cena vs. Batista in an "I Quit" Match...
World Heavyweight Champion Jack Swagger vs. Big Show... Edge vs. Randy Orton... Rey Mysterio vs. CM Punk in a SES Pledge vs. Hair Match
2011: Extreme Rules (May 1st) -
WWE Champion The Miz vs. John Cena vs. John Morrison in a Triple Threat Steel Cage Match... Christian vs. Alberto Del Rio in a Ladder Match for the vacant
World Heavyweight Championship... Randy Orton vs. CM Punk in a Last Man Standing Match... Cody Rhodes vs. Rey Mysterio in a Falls Count Anywhere Match... Michael Cole & Jack Swagger vs. Jerry Lawler & Jim Ross in a Country Whipping Match
2011: Over the Limit (May 22nd) -
WWE Champion John Cena vs. The Miz in an "I Quit" Match...
World Heavyweight Champion Randy Orton vs. Christian... Jerry Lawler vs. Michael Cole in a Kiss My Foot Match... R-Truth vs. Rey Mysterio
2012: Over the Limit (May 20th) -
WWE Champion CM Punk vs. Daniel Bryan...
World Heavyweight Champion Sheamus vs. Alberto Del Rio vs. Randy Orton vs. Chris Jericho in a Fatal Four-Way Match... John Cena vs. John Laurinaitis...
Intercontinental Champion Cody Rhodes vs. Christian
2013: Extreme Rules (May 19th) -
WWE Champion John Cena vs. Ryback in a Last Man Standing Match... Brock Lesnar vs. Triple H in a Steel Cage Match... Alberto Del Rio vs. Dolph Ziggler in an "I Quit" Match... Randy Orton vs. Big Show in an Extreme Rules Match
2014: Extreme Rules (May 4th) -
WWE World Heavyweight Champion Daniel Bryan vs. Kane in an Extreme Rules Match... Bray Wyatt vs. John Cena in a Steel Cage Match... The Shield vs. Evolution...
Intercontinental Champion Big E vs. Bad News Barrett
2015: Payback (May 17th) -
WWE World Heavyweight Champion Seth Rollins vs. Dean Ambrose vs. Roman Reigns vs. Randy Orton in a Fatal Four-Way Match...
U.S. Champion John Cena vs. Rusev in an "I Quit" Match... Sheamus vs. Dolph Ziggler...
WWE Tag Team Champions The New Day vs. Tyson Kidd & Cesaro in a Two out of Three Falls Match
Phew...