I'm finally getting round to reading Mary Douglas' 'Purity and Danger', regarding the connection between religious ritual and ideas of purity and impurity (to condense and simplify massively). It was a staple while I was at Uni, but I read in parts rather than right through depending on what I was studying.
On my too-read shelf I've Hobbes' 'Leviathan', Locke's 'Two Treatises of Government', a couple books by Niall Ferguson (I'm a fan of his pop-culture economic analogies and possible explanations for historical events), 'The Good Soldier: The Biography of Douglas Haig', and 'The Price of Inequality' by Joseph Stiglitz (he's always an interesting read, even if he sometimes suffers from the common political economist issue of spending more time poking holes in other people's ideas and theories than justifying his own alternatives).