There are quite a few collaborations I can think of when considering this question. I would like to start with a recent one, Gorillaz (Damon Albarn) and drum master, Tony Allen in the song How far. James Blake and Rosalía singing Barefoot in the park. The well known band from the late 90s and the begging of this century made an entire collaborations album called To All New Arrivals, which is worth mentioning. Last but not least, Poliça and Justin Vernon (Bon Iver) collaborated for the song Tiff as part of the Deluxe Version of Shulamith