I have 31 cookbooks, a large folder of magazine cuttings, 37 Cuisine magazines, and a folder of favourites on my laptop.
The books I use the most are Stephanie Alexander's Cook's Companion, Hugh F-W's Meat (transformed the success of my roasts, nom nom), several Nigel Slaters, Donna Hay, and Good Housekeeping.
Most of my books have at least one recipe that I use, e.g. Rick Stein's French Odyssey for cassoulet, Jamie for making pasta, etc.
I have four volumes of Larousse Gastronomique which I have to date found neither useful nor particularly interesting. Quite disappointing.
I am yet to use The Poacher's Handbook, but only because I am waiting for game season to start so I can try out the recipes.
The books I would most like which I don't yet have are the Simon Hopkinson ones.