Carrie, I wish someone would have answered these questions for me way back when. The texts used for AP Lit will vary from teacher to teacher, but mostly what I see fit the classical world lit category. Any work of significant literary quality can be used in an AP lit class. If your school is like mine, you won't have money for all new books, so some of what you choose for your class will come from the current stacks. Unless, of course, you are starting from scratch, and then you are in an enviable state (except, what to choose is the hard question).
Independent research on the academic benefits of the Advanced Placement English Language and Composition course indicates that not all students receive academic benefits from participating in the course. In a study with a sample size of over 90,000, the authors found that students who took the AP English Language and Composition course did not receive any increase in academic achievement unless they also prepared for and took the AP test. The authors controlled for over 70 intervening variables and found that AP students who took and passed the English Composition and Literature exam had ACT scores that were points higher than non-AP students or AP English students who did not take their course's AP test.  This led the authors to state that AP participation "... is not beneficial to students who merely enroll in the courses ..."  :p. 414