Subject encyclopedias can be invaluable as you begin to explore your topic. They give you a summary of research that has been done on the topic as well as explain terms and concepts that you're likely to run across. Many of the entries will also include bibliographies that point to important research in the field.
Handbooks provide information on a topic in an easy-to-use form. This can include data, procedures, methodologies, facts about organizations, and historical events. These tend to present quick answers to questions rather than a comprehensive overview.
Subject dictionaries give concise and accurate definitions of terms in that field. This is extremely important if you're researching a topic in which the same term may have multiple meanings in different contexts.
Reviews are articles that sum up the history of research on a topic and give you the current state of understanding. These have extensive bibliographies that will point you to influential papers on the topic.
Long articles on the history of study of a particular topic. Annual Reviews leads you to the most important and most read articles on your topic.
The International Encyclopedia of Human Sexuality by 
The Continuum Complete International Encyclopedia of Sexuality by 
The Oxford Handbook of Theology, Sexuality, and Gender by 
Oxford Encyclopedia of the Bible and Gender Studies by 
The Handbook of Language and Gender by 
A Dictionary of Gender Studies by