I agree with radiantshadow about the LHT (Surly Long Haul Trucker). It's super sturdy, even tank-like; its wheels even have more spokes than most bikes, and the components that come with the bike, while not highest-end, are of very good quality. It's a bit pricey new, though, and I've never seen a used one for sale; people who own them tend to hold on to them.