If your looking for a complete cheap bike, the redline monocog is kinda cool... and it's available as a 29er. But if your gonna spend some money, I might second the surly 1x1. Gary Fisher for '06 though came out with a vertical dropout, disc compatible, steel, eccentric bb, with a derailer hanger hardtail. Its available as a frame or complete geared bike I believe (sram x9 maybe...?). That could be a cool route.