My friend uses the Busch and Mueller Cycle Star mirror. I have some Cateye brand mirror that screws into the end of the drop bars. Both work well enough for our purposes. As mentioned earlier, the end of the drop bar is not a great location for a mirror on a touring bike but I've found an orientation where the view in the mirror clears the panniers in the back. Both of the mirrors are stiff enough to stay in place while riding while loose enough to shift position so as not to break if the bike should fall over on that side. In the name of science we've put this to the test several times...
I found the Cateye mirror for $8 at REI, so it's a good value. It says "Racing Mirror" on the back in fast looking font, but I'm not sure if it actually makes me any faster.