I love using an SM-57 together with a Royer R-121. The 57 captures the harsh, edgy rock attitude--it's just very present and in your face; while the 121 nicely rolls off all the high-end edginess, thus smoothing things out with warmth and body. I usually place each on different speaker types: one a a greenback, the other on a vintage 30, for example, make sure the phase alignment is balls on so there is no cancellation, and then run each through a high-quality preamp, panning one mic hard left, the other hard right. Between the natural differences in the mics and the speaker sources, together with the coloration of each preamp, the stereo field opens up. I also find use for AKG 414's and other various combinations, though the 57/121 combination is very good.