This always brings up an argument...but...Media Mail always worked for me with strategy guides. It's cheap, and, you can use a nice sturdy box to ship them in. (I was always able to get Delivery Confirmation on Media Mail, but, I've heard others couldn't.)
However, I don't officially know if they qualify or not. My post office always said they were fine for Media Mail. I even took some in once and had the postal worker flip through them and tell me they're good for MM. I've heard other people be denied on it.
As far as shipping, I always surrounded them a bit with a thin sheet of bubble wrap, and then, found a box that fit them snugly. Something that wouldn't get crushed, but also not something so extra large the guides floated around in them.