Most of my cookery is based upon a 'try it and see' approach, so I don't need any cookery books. (Indeed, I could probably write one myself if I could accurately remember all of the results of my experiments!).
However, if I need reminding about some of the basics (such as how to cook certain vegetables) I always fall back on my standard reference work, which has been in my kitchen cupboard for about 40 years:
http://thumbs1.ebaystatic.com/d/l225/m/mqCrYR2Zkyrth2O7ggei7Jg.jpg
I would probably also be using Mr Beeton's Book of Household Management, inherited from my mother (who referred to it for nearly all of her cooking) if I'd not made the mistake of lending it to a friend who treated loans in the same way that she treated all of her birthday and Christmas presents. (i.e. as something to be offered for sale at the first available car boot sale!)