Nirvana had many different lineups until they settled on the legendary one that everyone knows of:
Kurt Cobain: vocals, guitar
Krist Novoselic: bass
Dave Grohl: drums, backing vocals

Anywayz, here's everyone who was a part of the development of Nirvana....

Kurt Cobain: vocals, guitar (1985-1994)
Krist (Chris) Novoselic: bass (1985-1994)
Aaron Burckhard: drums (1985-1986)
Dale Crover: drums (1988)
Chad Channing: drums (1986-1990)
Jason Everman: guitar (1989)
Dave Foster: drums (1988)
Dan Peters: drums (1990)
Dave Grohl: drums, backing vocals (1990-1994)
John Duncan: guitar (1993)
Pat Smear: guitar (1993-1994)