Last weekend I decided to master crochet once and for all, so I decided to buy this book from Amazon. I've got to say that I am really impressed. It explains everything in detail - I'm sure a child could learn to crochet from this book. There is only one drawback though - it's American and their crochet terms are completely different to ours!
However, for anyone wanting to convert American crochet patterns to British, these is a conversion chart in the book.