In my work I am frequently working with self-organizing teams. This problem with consensus comes up frequently. One of the best solutions to the problem is to have a very clear long-term goal or vision that everyone agrees to. In corporate environments, this is usually imposed. In a coop or other volunteer situation, it can be difficult to articulate this goal, but the effort in getting there is worth it. Once the goal is in place, it is (relatively) easy to get consensus on decisions if they are relevent to the goal. If the group is trying to decide on something irrelevent to the goal, then again consensus is very difficult, mostly because the decision "doesn't matter".