There are several artist going by this name:

1) Plan 9 is an American neo-psychedelic band from Rhode Island formed in 1979.
The group was named for the 1950s science fiction film Plan 9 from Outer Space.
The Calgary Herald wrote, in 1989, "Its music has that spirited, no-holds-barred feel of rock from the '60s while managing to not sound dated.

2) Wellington (New Zealand) based composers Plan 9, consisting of David Donaldson, Steve Roche and Janet Roddick, have scored music for an impressive array of film, television, installation and theatrical projects. Plan 9, in collaboration with David Long, composed the cultural music and the music/sound of “The One Ring” for Peter Jackson’s Lord of the Rings trilogy. The group has also created ambient music design for Jackson’s King Kong. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.