Google is working on a project to scan and make available all of the books ever written.

I just came across some study guides that they have scanned already.

This link is to the REA US History I CLEP study guide. It is from 1995, so I’m not sure if this is too old for our purposes.

The best test preparation for the ... - Google Book Search

On the same page, they also have links to more study guides, and with a search, there are probably more to be found.

Again, I’m not sure if this is too old, but it could be good extra material, if needed.

Best wishes on your studies!

NAP

Update: I just looked at these again. A lot (if not all) appear to be limited preview items, which means you can not read the whole book using this website.