In honor of Valentine's week, Billboard has compiled a list of the biggest duets of all time -- and coming in at #1 is "Endless Love," by Lionel Richie and Diana Ross. The magazine came up with the list by ranking each song on a point system based on its performance on the Billboard Hot 100 chart: the more weeks a song spent at #1, the more points it would get. In addition, each song had to be a true duet, with equal vocal time given to both singers. "Endless Love" won because it spent nine weeks at #1 and stayed on the over chart for 27 weeks which, back in 1981, was a very lengthy run.

The song that came in at #2 on Billboard's list isn't exactly a love duet -- it's "Say, Say, Say" by Paul McCartney and Michael Jackson. Paul's other famous duet with Stevie Wonder, "Ebony & Ivory," is in at #4, just behind Brandy & Monica's "The Boy Is Mine." Here's the rest of the top 10:

5. "Dilemma" -- Nelly & Kelly Rowland
6. "I'm Real" -- Jennifer Lopez & Ja Rule
7. "My Boo" -- Usher & Alicia Keys
8. "Baby Boy" -- Beyonce & Sean Paul
9. "Islands in the Stream" -- Kenny Rogers & Dolly Parton
10. "Don't Go Breaking My Heart" -- Elton John & Kiki Dee

Other songs that made the list farther down include "No Air," by Jordin Sparks and Chris Brown; "All I Have," by Jennifer Lopez and LL Cool J; "The Girl is Mine," by Michael Jackson and Paul McCartney; and, of course, "I've Had the Time of My Life," from Dirty Dancing, featuring Bill Medley and Jennifer Warnes.