Raisin Hell by Run DMC fused Rock and rap together which influenced such groups as Cypress Hill, and Rage Against The Machine among others
NWA Straight Outta Compton spawned gangsta rap and put the Westcoast on the Map for good
Ghetto Boys (same as Geto Boys) Grip it! On that other Level, even more hardcore than NWA, spawned Scarface and represented Texas
EPMD classic samplers of beats are now the most sampled hip hop group of all time. These guys first two albums were deliciously "funky" absolute classics
Public Enemy It takes a nation..... best political rap album ever
BDP/KRSONE by all means necessary, criminal minded, social consciousness to hip hop and brilliant for its time
Dr. Dre The Chronic, simply put, g-funk birthplace, and an amazing collaboration of artists all living together in a studio
Snoop Doggy Dog - Doggystyle, most anticipated album of all time, classic g-funk with snoops low key drawl
Eric B & Rakim, there was a time when no one flowed better than Rakim
2 Live Crew around the time of NWA, they were also making waves with their sexed out lyrics and miami bass sound
Tupac and Biggie are both overrated, unfortunately due to their passing. Both put out great music, with completely different styles, and many regard them as two of the greatest emcees of all time.
Groups like de la soul, jungle bros, etc, also created a less violent sound, which more people link to Hip hop, rather than rap (a whole different debate).
Either way, the stuff out today (its all about bling) pales in comparison to what came out in the late 80's and early 90's.
I think what is really differnt other than the bling, is that the production and beats on today's records arguably have a more club like feel, whereas the old hip hop/rap beats were a little more unrefined.
just one mans opinion