Rez, those are good choices. Also look into:
Non Phixion (!)
Jedi Mind Tricks
Boogie Down Productions / KRS-One
Cormega
Dead Prez
Gravediggaz
Deltron 3030 (Del tha Funky Homosapien and Dan the Automater. Kind of like a sequel to Dr. Octagon, which you should also get)
Sunz of Man
GZA/Genius
Inspectah Deck (Uncontrolled Substance is one of the best rap albums ever)
Canibus
Timbo King (a lot of rare stuff, but if you can find it it's really good)
A Tribe Called Quest
Slick Rick
Talib Kweli
Those are just a few
