I have a color turbo. Wonderful. Nearly useless, but wonderful. I would like a Cube so that I can relive the wonder of its release at a Seybold tradeshow way back when I was early in my career.
Great resources and discussion board here: http://www.nextcomputers.org
Really if you have any NeXT software you should make copies and share with the world.
GNUSTep is an implementation of the Openstep spec, so there's a good chance that that old software could be ported to Linux (or even OSX) without too much effort.