Another vote for the Joy. I've referred to it as the bible, its something you can always reference if you don't know how long to cook a turkey, convert some measurement, prepare dry beans among a million other things, just an awesome basic.
I received The Tao of Cooking as a gift while in college and still use it very often (10 yrs later). It's veggie (I'm not), but a really nice well-rounded collection of a lot of different ethnic dishes.
My rule for buying cookbooks is to flip through, look at a few recipes and if you see the words margarine, non-stick cooking spray or microwave, put the book down and keep on looking. I find that these try to be the "healthy" and "light" books, to which my reply is: NOT. (just ignore this if you don't agree)