Formed: 1988, Billy Corgan & James Iha
Albums: Gish (1991), Siamese Dream (1993), Pisces Iscariot (1994), Mellon Collie & The Infinite Sadness (1995), Adore (1998), MACHINA/the machines of God (2000), MACHINA II: Friends and Enemies of Modern Music (2000)
Members (in order of joining): Billy Corgan, James Iha, D'arcy, Jimmy Chamberlin
Significant Contribution to Musical World: One of the leading rock acts for over a decade; the Pumpkins' musical expression has touched fans worldwide, outlasting other "alternative" acts such as Nirvana or Soundgarden. They have received multiple awards ranging from MTV's Video Music Awards to the Grammies. Their legion of fans is a highly dedicated following with a (usually) close personal connection to the band. Not your usual cup of alternative tea, in other words.

A bit more on the other members of James Iha's second (and assuredly most influential) band . . .

D'arcy - Jimmy Chamberlin - Billy Corgan

Some GREAT Pumpkin sites to check out:

Siva
Netphoria
2007.org
Smashing Pumpkins Fan Collaborative
Smashing Pumpkins Internet Fan Club