Handbook of American Women's History (R305.4 H191) An excellent place to begin when one is new to a topic in the field. It includes "...summary definitions with focused bibliography for crucial concepts, events, organizations and various historical persons" (from the Introduction).
Women's Progress in America (R305.4 F92a)
Women's Studies Encyclopedia. Vol. III: History, Philosophy, and Religion (R305.4 W842t v.3) Good introductions to such broad topics as "Immigrant Women," "Antislavery Associations," and "Women's Rights Movements"); volumes I and II of this set cover "Views from the Sciences" and "Literature, Arts, and Learning," respectively.
Susan B. Anthony Slept Here: A Guide to American Women's Landmarks (973.082 Sh5s) Arranged by state, and then by city, this nicely illustrated volume introduces the reader to about 2000 landmarks.
Women Remembered: A Guide to Landmarks of Women's History in the United States (R917.304 T49w)
The New Quotable Woman (R808.8 Q57a 1992)
The Book of Women's Firsts (R920.72 R22b 1992)