as far as hip hop goes:

how could no one mention tribe? who ARE you people?!

a tribe called quest: any and every album (even "the love movement")
de la soul: stakes is high
quasimoto: the further adventures of lord quas, the unseen
method man: tical
ol' dirty bastard: return to the 36 chambers, the dirty version
wu-tang: enter the 36 chambers
madvillain: madvillainy
viktor vaughn: vaudville villain
mobb deep: the infamous (amoung others, but if you only want one album, get this one)
outkast: Southernplayalisticadillacmuzik, ATLiens, Aquemini, after that andre went crazy and the music suffered)
Soundbombing part 2
O.G.C.: da storm
heltah skeltah: magnum force
smif-n-wessun: dah shinin
prince paul:a prince amoung thieves

that should at least get you started.