There is “Bring The Noise” that is Anthrax with Public Enemy so its thrash metal w/rap if that will work.

One that blows me away cuz its so weird i/m/o is Bryan Adams doing a duet with Barbra Streisand!!!! Talk about different types of voices haha and the song is “I Finally Found Someone”

Or even when David Bowie did the christmas duet with Bing Crosby , wow who would have ever thought that would be a combo!! And that song was “Little Drummer Boy”

Or how about Huey Lewis singing with Gwyneth Paltrow from the movie “Duets”, and it was pretty damn good too. Song was “Cruisin”

annnnnnnd Celine Dion with R. Kelly doing “Im Your Angel”

Not sure if this will fit since they were both kind of pop artists but Phil Collins and Philip Bailey( from earth wind and fire) doing “Easy Lover”

Hope that helps.

Dead and gone – T.I. and justin timberlake
Stan – Eminem and Dido
Fast Car – Wyclef Jean and Paul Simon
yea thats all i can think of