Unknown DJ

Andre Manuel, the Unknown DJ, early west-coast electro beats.
"Basstronic" single, 1988:

better audio: http://youtu.be/ytddqtWSP-E

Afrika Bambaataa & the Soulsonic Force

Afrika Bambaataa & the Soulsonic Force were instrumental in the development of hip-hop (Afrika actually coined the term) and electro-funk with their unique blend of European electronic music, american funk, and rap. They helped push hip hop to the forefront of American dance music, and were one of the first hip hop groups to carry strong (and positive) political and social undertones.
"Looking for the Perfect Beat" video for the 1983 single:

"Planet Rock" from the 1982 Planet Patrol/Soul Sonic Force split EP:

"Renegades of Funk" video for the 1983 single:

A Tribe Called Quest

"Electric Relaxation" from the 1993 album Midnight Marauders:

Grandmaster Flash & The 4 MC's

mixtape of a live set from 1978 when hip hop was still a baby:

Black Sheep

"Without A Doubt" from Non-Fiction (1994):

A Tribe Called Quest

from the album Low End Theory (1991), "Jazz (We've Got)" and "Buggin' Out":

Eric B. and Rakim

"In the Ghetto" from 1990's Let the Rythm Hit 'Em.

Medusa

the emcee goddess, Medusa with "power to the P," underground hip hop from early 1990's Los Angeles.

The Pharcyde

1993 single "4 Better Or 4 Worse." thanks to Lamaraba for turning me on to this.