Sumo: A Pocket Guide by Walter Long (C.E. Tuttle Co., Rutland, Vt., 1993, ©1989)
This is a good brief introduction to sumo. I read the 1989 first edition, so it's a little outdated in terms of some of the rikishi mentioned who were active at the time of writing. Chapters cover the history of the sport, life in the stables, the climb to the top, the Grand Tournament, the role of the yokozuna, the meanings of names, the referees and judges, salaries and other compensations, and tips for watching sumo. It also includes a glossary of sumo terms, addresses of "chako-nabe" (the stew that is the staple food of sumo wrestlers) restaurants, and the addresses of the stables (outdated information by this time). It's the first book on sumo I've read so I can't compare it to any others, but I would gladly recommend it as it stands for a good introduction to the national sport of Japan.