"The Best Things in Life Are Free" is a duet between American singers Luther Vandross and Janet Jackson, recorded for the Jimmy Jam and Terry Lewis-produced soundtrack to the 1992 American film, Mo' Money, starring Damon Wayans. It was later included on the compilations Design of a Decade: 1986 -- 1996 (1995), One Night with You: The Best of Love, Volume 2 (1997), Lovesongs (2009) and Number Ones (2009). The song was composed by Jam, Lewis and New Edition / Bell Biv DeVoe members Michael Bivins and Ronnie DeVoe.

Who sang best things in life are free? OK. Let's think. My stream of consciousness:
The relevant information to answer the above question is: "The Best Things in Life Are Free" is a duet between American singers Luther Vandross and Janet Jackson, recorded for the Jimmy Jam and Terry Lewis-produced soundtrack to the 1992 American film, Mo' Money, starring Damon Wayans. The answer is American singers Luther Vandross and Janet Jackson.