Cyclingnews.com and their coverage of Eurobike 2008 have brought to my attention the Salsa Fargo. It's not particularly light or fast, it doesn't have 6 inches of suspension travel, and none of the materials it is made from have ever been launched into space. It is so boring it's exciting.
-29er wheels (so it might not be for everybody)
-tons of braze-ons
-disc brake tabs
-huge fender/tire clearance
Ride it on trails, ride it to work, ride it from the Pacific to the Atlantic, put a trailer on it and ride your kids to preschool. Have a set of road and a set of off road wheels and you could make do with just this one bike for everything.
picture from salsacycles.com