I'm going to pick a underground rapper name Snacky Chan because he raps about issues facing Asian-Americans. Check out his song "Part of the Nation" here. Lyrically I think he is better than Jin, the more well known Asian rapper.
Talib Kwelli's first album. Any TCQ, although I don't think they were really all that socially conscious - just not thugs.
KRS One's Edutainment is the most informative rap album I've ever listened to and I can't find it anywhere.