I guess it depends on what you want to cook but I have Jamie's ministry of food which I find is great for soups, sauces and roasts but it's way far from the healthy eating which he so promotes but is pretty much the modern day bible. Everything is laden with fat so beware it's not a healthy cook book.
I also have James Martin's Great British Dinners which is a few years old now but really good for stuff like stews, pies, goulash, stroganoff, duck, game and puddings. Also one called Brian Turner's Favourite British Recipes which has given me a few ideas for things like perfect yorkshire puds and pastry.
Ken Hom for chinese although I never think you can truly create chinese like the takeaways so I tend to stay away from chinese cooking at home unless you have a nearby chinese wholesaler. Madhur Jaffrey's
An invitation to indian cooking is a must.
But the one i'm reading right now is the slimfast free foods book where i've found the perfect recipe for chicken tika massala.
I really want to get a river cottage book as the recent series has given me some great recipes.
Personally I don't think you can ever choose just one book. You have to have a selection of at least half a dozen or more.