The CLEP Study guide is pretty much right on.
The Peterson's test has a lot of excess junk that's not on the CLEP test in my experience, mainly biographical questions about the authors.
If you're using the Complete Idiot's Guide to American Literature as the main study source (which is the general consensus as the best resource for the test, apparently,) I would use Wikipedia and other websites to browse a few passages by different authors.
And don't skip the Native American writers section.
Allow me to introduce myself. My name is Wile E. Coyote, genius. I am not selling anything nor am I working my way through college, so let's get down to basics: you are a rabbit and I am going to eat you for supper. Now don't try to get away, I am more muscular, more cunning, faster and larger than you are, and I am a genius, while you could hardly pass the entrance examinations to kindergarten, so I'll give you the customary two minutes to say your prayers.
Now officially a holder of a Bachelor of Science in PsychoRabbitology degree
Currently enrolled in Concordia University - Portland's Master of Education with a specialty in Rabbit-specific destructive munitions (or eLearning & Technology, I forget which)