RZA, J-Dilla, Kev Brown, Nottz Raw, Evidence of Dialated Peoples, Big K.R.I.T., Diamond D, Damu The Fudgemunk, Flying Lotus, Tyler The Creator, JonWayne, Pete Rock, Heavy D, Kaimbr, Oddisee, MF DOOM, Madlib, Necro, El-P, Ill Bill, Aesop Rock, Black Milk, Jay Electronica and so forth. There are more than a handful of producer/ rappers. Its just a balancing act. How much effort do i put into beats and how much into lyrics? But there will always be a producer who tries to rap or sing just like there are rapper/ singers who try to produce. Doesn't mean they all should but it's all in their creative ability though.