Wright was one of the members that founded the group circa 1966.
His playing can be heard on most of the group's albums, but maybe most memorable on the first one, The Piper at the Gates of Dawn, and the huge 1973 success Dark Side Of The Moon.
http://www.pinkfloyd.co.uk/ has published this short message:
"The family of Richard Wright, founder member of Pink Floyd, announce with great sadness that Richard died today after a short struggle with cancer. The family have asked that their privacy is respected at this difficult time."
Pink Floyd guitar player David Gilmour writes this on his website http://www.davidgilmour.com/:
"In the welter of arguments about who or what was Pink Floyd, Rick's enormous input was frequently forgotten.He was gentle, unassuming and private but his soulful voice and playing were vital, magical components of our most recognised Pink Floyd sound."
UPDATE September 20: Timesonline has published the last interview with Rick, done back in 2007. Read it here.