Sam Harris has a good book on this where he goes over both the philosophical arguments against free will (he argues that free will is an illusion) and some neuroscience data showing how our brains actually make our decisions before we are even conscious of them. He also pontificates how if you really think about it, you can experience for yourself how certain thoughts appear seemingly out of nowhere, for instance if asked to say the first city, or vegetable or whatever, to pop into your head. These mental 'whims' are for the most part non-conscious.
Another good point he makes, that has been mentioned in this thread already, is that an argument against determinism by pointing out possible examples of randomness (quantum physics etc.), is not an argument for free will at all, it just means that we are governed by chaos instead of causality, but still not by ourselves.