I really appreciate Susan Wise Bauer's The Well Trained Mind. I've used and used it. One of the things I like is how many ideas and options she gives for each stage of learning. For middle school, I require my kids to use some primary sources. She gives an easy way to evaluate them.
How it works for us, is that I find (or let them find) a primary source online. Here are a few:
I've also found this article interesting, but for ease of use you can't beat The Well Trained Mind's evaluation of primary sources. Thank you Susan Wise Bauer!!