There was just a pretty big thread on this:
http://www.acousticguitarforum.com/f...d.php?t=206837
I think lots of mics can work, but it depends on your situation, sound system, etc. Here's Eric Skye using an AKG mic, along with a K&K in a performance last weekend. This sounded great in person.
http://www.youtube.com/watch?v=ZC5uHqjY9QM
I often use a DPA 4099, clips to my guitar, and it also works very well, but I also generally use a pickup along with it. You can blend to taste, and as feedback issues and so on allow.
When you start listening to things like the Dixie Chicks on a DVD, keep in mind how much major money and sound engineering talent went into getting that sound. You with a combo amp in a small club or coffee house are not really dealing with the same set of tools.