Seconded on "The Joy of Cooking"; it covers topics from the very basic to the very advanced. I found the left-hand side of that spectrum extremely useful when I was just starting out cooking, when I had "silly" questions like:

• What does "broiling" mean?
• What should a decent cutting board be made of? (There are a surprising number of cutting boards out there that are made of totally useless materials like glass).
• How do I tell a good tomato from a bad one?

And so on, all those things that it seemed like I ought to already know, but didn't.