If you want to add some carrying capacity to your hardtail that's equipped with disc brakes, check out Axiom's Odyssee Disc Rack. Aluminum components ensure strength, stiffness and durability for the long haul. The rack also fits 24 to 28-inch wheel sizes thanks to articulating and telescoping stays.
Capacity: 55 pounds (25 kilograms)
Also available in Silver (image unavailable form manufacturer).