I recently tried out a great micing technique for guitar cabs involving a dynamic and a large diaphragm condensor used together. I used an SM57 and a CAD M37. Have them pointed in an X configuration so each mic is angled diagonally compared to the face of the guitar cab and pointed towards the wall of the speaker. When I tried this I wound up situating both mics basically in front of the center of the cone, but angled so they weren't actually pointing at the cone. You have to mess around a little bit to make sure they're not out of phase with each other, but once you do you get a really big guitar sound. I only got to record a snippet like this, and it was a good sound but I wanted a few more highs so the next time I'll probably point the mics more towards the center of the cone.