Really this is Phantasmatron's thread since he had the idea for it in the other thread
https://www.dreamtheaterforums.org/boards/index.php?topic=10501.0 but I didn't feel like waiting for it to become a thread so here we go. My first suggestions:
Biz Markie on Wait for Sleep since he's money on piano tracks:
Just a Friend https://www.youtube.com/watch?v=r6a-AHLRoAwJohnny Cash on Take the Time since it'd be priceless to see him sing the "If there's pensive fear, a wasted year" part 14 octaves lower
Stephen Hawking on instrumentals
Mase for Light Fuse and Get Away since I'm sure his head actually explodes if he has to sing quarternotes faster than 80 bpm
Alrighty folks, now's your turn!