Nelly's 'Over and Over' (September 2004)
Nelly had his initial breakthrough with the southern-accented album Country Grammar, and went on to become a go-to crossover collaborator for country acts. First he brought in Tim McGraw to croon the brooding hook of "Over and Over" and appear in the song's split-screen music video. A decade later, Nelly guested on a bona fide blockbuster remix of Florida Georgia Line's "Cruise." He's not an isolated crossover case. Also around that time, pop-savvy Atlanta rapper B.o.B tapped Taylor Swift to sing on his single "Both of Us."