This is basically a spinoff of the best rapper of each year thread:
1990- Marley Marl (produced the Mama Said Knock You Out album)
1991- Dr. Dre (co-produced nikkaz4Life)
1992- Pete Rock (produced "T.R.O.Y". I know he did the whole album from which that song came, but even still "T.R.O.Y" is so iconic on its own)
1993- Dr. Dre ( produced Snoop's Doggystyle and The Chronic carried over from '92)
1994- DJ Premier (his work on Illmatic, Biggie's "Unbelievable", Jeru's Sun Rises In The East, and Gangstarr's Hard To Earn is quite a run)
1995- RZA (epic producer run in Hip Hop considering he produced OB4CL, Liquid Swords, and Return to the 36 Chambers all in this same year)
1996- Trackmasters (helped It Was Written, still had some tracks from LL's Mr. Smith that carried over, and there's Foxy's Ill Na Na)
1997- The Hitmen (completely dominated considering they produced Biggie's Life After Death, Puff's No Way Out, and Mase's Harlem World. Love them or hate them, this was their year)
1998- Beats By The Pound (23 albums in one year. What a run. Again, love them or hate them. They ran '98)
1999- Mannie Fresh/Swizz Beatz (This could go either way because it was like they were battling for that #1 spot in 1999)
1990- Marley Marl (produced the Mama Said Knock You Out album)
1991- Dr. Dre (co-produced nikkaz4Life)
1992- Pete Rock (produced "T.R.O.Y". I know he did the whole album from which that song came, but even still "T.R.O.Y" is so iconic on its own)
1993- Dr. Dre ( produced Snoop's Doggystyle and The Chronic carried over from '92)
1994- DJ Premier (his work on Illmatic, Biggie's "Unbelievable", Jeru's Sun Rises In The East, and Gangstarr's Hard To Earn is quite a run)
1995- RZA (epic producer run in Hip Hop considering he produced OB4CL, Liquid Swords, and Return to the 36 Chambers all in this same year)
1996- Trackmasters (helped It Was Written, still had some tracks from LL's Mr. Smith that carried over, and there's Foxy's Ill Na Na)
1997- The Hitmen (completely dominated considering they produced Biggie's Life After Death, Puff's No Way Out, and Mase's Harlem World. Love them or hate them, this was their year)
1998- Beats By The Pound (23 albums in one year. What a run. Again, love them or hate them. They ran '98)
1999- Mannie Fresh/Swizz Beatz (This could go either way because it was like they were battling for that #1 spot in 1999)