Zöllner's 'The Complete Paintings and Drawings', published by Taschen, is one of my favourite books. In fact, it's two books – one for paintings, and one for drawings – and a complete collection of everything that survives from Leonardo's work. There are apparently still lots of codices that are missing, unless they've already been destroyed.
As it's a full collection, everything from the scrappy doodles to the finished paintings is included. Modern exhibitions of his work lead us to believe he was a portrait artist who achieved nothing but perfection. So, it's amazing to see some of the more amateur drawings he produced (which we never find on display) and to notice that so many of his drawings were actually mechanical schematics which were the result of his working for Cesare Borgia and other military leaders.
The only downfall to the books is that they're presented inside a cardboard casing that isn't the best quality. If you look closely at the first image, you can see the vertical lines in the cover – the cardboard texture showing through. Not the best design decision given the price of this otherwise brilliant book.