What cookbooks do you always come back to?
Definitely the Joy of Cooking.  It's not a convenience cookbook for people with busy schedules or low patience - the majority of recipes in there are geared toward flavour and not specialty diets or quick prep times - but at least 9 out of 10 recipes I try in there have near-perfect flavour and texture.

IMO, this should be in every cook's kitchen, even the ones that don't really use cookbooks.  It has all the classic recipes, and you never know when somebody will ask you to make Chicken Kiev.