There are three main types. Each is a vibrant field of critical debate, but on the GRE Literature exam, you'll rarely be asked to do more than identify a caricature almost certain to include the buzzwords below.
1. Feminist Criticism
-phallocratic hegemony, patriarchy
2. Black Criticism
-Euro-American patriarchy
3. Post-Colonial Criticism
-subaltern; marginalization of the other
-Edward Said, Orientalism
For more information, I recommend Culler's Literary Theory: A Very Short Introduction