Sorry to present a bit of discontinuity in this discussion, but a few people might be wondering why I seem to be arguing for free will despite having nailed my colours firmly to the mast before now, arguing from a very much anti-dualist, anti-spiritualist viewpoint. OK, so probably no-one was wondering that, but indulge me for a moment...
I'm sure everyone would agree that lumpen, inorganic matter has no 'free will' - there are processes whose outcomes are perhaps impossible to predict due to computational difficulty (stochastic processes) or those which are, even in principle, inherently random (loosely, quantum 'measurements') - but these cannot be said to impart 'free will', just blind, physical indeterminism. Now some people might believe free will and other qualities such as consciousness are imbued into matter by some kind of spirit or soul, although I certainly don't hold this position. But is it possible that free will is an emergent property of a sentient mind, just as sentience seems (to a non-spiritualist) to be an emergent phenomenon? I mean, no-one would claim that a simple electrical circuit, or even a modern supercomputer, is conscious or has genuine intelligence (as opposed to powerful circuits running intelligently-written algorithms). Yet through some physical means or other - sheer complexity according to some, quantum-gravitational effects(!) according to Roger Penrose - there appears to be a property variously called intelligence, sentience or self-awareness in human brains - and to be quite honest, no-one really has the faintest idea how it happens.
So if we are prepared to believe that a lump of warm wet goo can give rise to intelligence, without appealing to some nebulous anima, is it really that much of a stretch to consider that maybe volition arises in the same way - perhaps even that volition is a necessary consequence of, or complement to, understanding and intelligence?