I cant pick one over all so mine go like this:
Beginning techniques: Jacques Pepin's Complete Techniques, and CIA The new Professional Chef.
Everyday cooking: Best Recipe, Cooks Illustrated
Italian: Made In Italy, Giorgio Locatelli
French: Lutece, Andre Soltner, New Entertaining in the French Style - Roger Verge, East of Paris - David bouley and MAFC - Julia Child
Over the Top, not that practical but total eye candy and inspirational: Alinea, The Fat Duck, Under Pressure, A day At El Buli, Grand livre de Cuisine, CIA Frozen Desserts. This can get dangerous and lead to bulging cookbook shelfs and waistline and really expensive kitchen remodel as well as lots of cooking apparatus that make my counter tops look like a science project.
my wife and friends love all the meals I make from hundreds of books so as you can see its very hard for me to choose.
Cook with love! - then it really doest matter what book your reading