These two books are probably not on the market, though 'classic' in terms of information.

1) Whittle, A., Pollard, J. and Grigson, C. 1999. The harmony of symbols: the Windmill Hill causewayed enclosure. Oxford: Oxbow Books. Gives the full and interesting account of the Alexander Keiller excavations (and other excavations) on Windmill Hill.

2) Sacred Mound, Holy Rings: Silbury Hill and the West Kennet Palisade Enclosures - A Later Neolithic Complex in North Wiltshire (Oxbow Monographs in Archaeology) [Paperback] A.Whittle with contributions by J.Best.. £46 quid on Amazon if you are not boycotting..

The causewayed enclosure at Windmill Hill was excavated by Alexander Keiller, and there are some fascinating insights into the bones found in the excavation, lost my copy sadly....