agreed on all optimum's suggestions for Neptunes - Clipse albums especially, much darker than a lot of their stuff though
some other personals:
Missy - On & On
Daft Punk - Harder Better Faster Stronger Remix
Busta - Call The Ambulance
Busta - Pass The Courvoisier Part II
Snoop - Beautiful
Snoop - Drop It Like It's Hot
Timbaland masterpieces are too many, its hard to know where to start!
his Aaliyah and Missy productions are my favourites though i think
also
Genuwine, and hundreds of miscellaneous