In addition to many already named, Tracey Lee. Many Faces was a more than solid debut.
I don't know how well Suga Free's music is recognized outside of the west coast, so I'll add him with an asterisk. If I'm wrong, and he gets bumped all around the country let me know.
Some good responses, but I question some of people's definition of never "blow up" especially when some of the people mentioned had successful careers, considered legends, and were known nationwide to most.
Black Moon
Big Mike
No I.D.
Bahamadia
Boss
Spice 1
Coup
LOTUG
Souls of Mischief
Digable Planets
Organized Konfusion
8Ball & MJG
O.C.
Jeru Da Damaja
Camp Lo
Dayton Family
Tela
Project Pat