Mercenaries
Blackwater USA, a company that has been providing private security forces in Iraq announced that they could provide a brigade sized unit any where in the world. They were available for security and peacekeeping rather than combat roles. One suggested use for a force such as this was Darfur, where the African Union troops are dismally ineffectual and no one else is willing to step up and send troops to the regions.
The Strategy Page pointed out that the UN and NGOs already use private security forces, often recruited locally and of varying quality. This would suggest that a larger scale application of the principle may be acceptable. One main drawback is that many of the nations that regularly hire out military forces to the UN for peacekeeping make a significant profit on the deal and will likely object to the competition.