Stephen Turnbull. Samurai Heraldry. Osprey Publishing, 2002. (excellent English intro with dates and usage information)
John W. Dower. The Elements of Japanese Design: A Handbook of Family Crests, Heraldry & Symbolism. Shambhala Publications, 1990. (explains the symbolism and brief histories of many crests, but light on details)
An Illustrated Encyclopedia of Japanese Family Crests. Graphic-sha, 2001. (one of many mon collections; this one has good variety and crest names in both kanji and kana)
Taniguchi Gyokusen, Sekigahara Gosen ni Manabu (Houzouji, 1983)