Top 5 Producer-Rappers (i.e. primarily known for their production work) of all time:
5. Pete Rock - Not a very good rapper, but he doesn't embarrass himself too often.
4. Kanye West - Would have put him higher, but his lyricism and technique have been declining steadily since College Dropout.
3. Dr. Dre - This guy might be number one if he actually wrote any of his lyrics.
2. The RZA - Tends to put out a lot of really shitty stuff, but when he's on, he's on (see anything he's done with Ghostface).
1. El-P - Very consistent, always has something interesting to say, and I agree with his overall worldview that everything's going to shit, and there's nothing we can do to save it.