On October 22, the Cato Institute will host a conference on the subject of "Lessons from the Iraq War: Reconciling Liberty and Security." Much of it will be a re-hash of the war in Iraq. But Panel III -- "The Principles Guiding Military Intervention" -- might offer some useful libertarian insights for and against pre-emptive war.
For some of my neolibertarian views on the subject, try these posts:
Libertarian Nay-Saying on Foreign and Defense Policy
Libertarian Nay-Saying on Foreign and Defense Policy, Revisited
Libertarianism and Pre-emptive War: Part I
Right On! For Libertarian Hawks Only
Understanding Libertarian Hawks
More about Neolibertarianism
More about Libertarian Hawks and Doves
Defense, Anarcho-Capitalist Style