I can't say enough about this beautiful little bilingual book. When combined with Ash Warren's The Way of Salt, which provides a lot of philosophical background for the sport, the 34th Kimura Shinosuke's "Perfect Guide" delivers everything else you need for a proper nuts-and-bolts understanding of the one true martial art. The fact that it's laid out so beautifully, with dozens of traditional woodblock prints depicting 19th-century sumo scenes, is a bonus.
In short, it's been great toilet reading for the past two months. Easy to pick up, easy to put down. Highly recommended if you're getting into sumo.