A wide variety of things come in groups of four, such as the major tennis tournaments (the French Open, Wimbledon, the Australian Open and the U.S. Open). Some other examples include the rocky planets in the Solar System (Mercury, Venus, Earth and Mars) and the Four Humors (blood, yellow bile, black bile and phlegm).
There are four major mathematical operations (addition, subtraction, multiplication and division), four DNA nucleobases (guanine, cytosine, adenine and thymine), four gospels (Matthew, Mark, Luke and John), four major U.S. sports (football, baseball, basketball and ice hockey), four Indiana Jones movies as of 2014 ("Raiders of the Lost Ark," "Temple of Doom," "Last Crusade" and "Kingdom of the Crystal Skull") and four instrumentalists in a classical string quartet (two violinists, a violist and a cellist).
In addition, there are four seasons (winter, spring, summer and fall), four cardinal directions (north, south, east and west), four Greek classical elements (air, earth, fire and water), four Ninja Turtles (Donatello, Michelangelo, Raphael and Leonardo), four nations in the United Kingdom (England, Scotland, Wales and Northern Ireland) and four cardinal virtues (justice, prudence, fortitude and temperance).
There were four members of the Beatles (Lennon, McCartney, Harrison and Starr) and four major characters in "Seinfeld" (Jerry, George, Elaine and Kramer). There are four limbs on the human body. Major world sporting events, such as the Olympics, the FIFA World Cup and the Rugby World Cup, occur every four years.