When I studied for the CLEP Western Civ 2, I used the Princeton Review's AP for European History, which I got at the library. Because I was studying Civ 2, I only read the second half. Presumably, the first half will work for the Civ 1 test, too.

I don't know whether the AP guide is any better than REA's CLEP guide, but it seemed to work for me.

I like the way you use flashcards for study. That sounds like an excellent method - it makes your brain more active.