Random Link: The trouble with the SM57 is, it sounds mediocre to passable to good, depending on how it's set up, but it never sounds great, like other, newer microphones. So often it's a lot easier to mount and record with a new (sometimes cheaper) microphone than bother with the SM57's boxy sound.
There's a bunch of instrument dynamic microphones that compete with the SM57, and we're not talking about the cheap clones. The AKG D-40 is a specialised instrument microphone that many adore on toms, but it also records just about any drum and guitar cabs nicely. It misses some of the HF detail compared to a modded SM57, but it is warmer, quicker, and works better with small percussion (it even records crotales well). Audio-Technica ATM650 might be an option too. And there're those Beyerdynamic microphones, though they're expensive.
SM57 defenders will often say they work for anything, and professional studios often have a few lying about. True, but then professional studios also have mighty fine preamps. Unlike the lonely fellow who buys an SM57 to plug into a mono sound interface preamp. They say the SM57 sounds great through a good preamp; the downside here is, said preamp is at least five times as expensive as the microphone itself. Oh sure, professional engineers will drivel about how great records can be made with cheap gear. How you, the low-budget fellow, can spend very little, the $100 condenser and the $100 SM57. The flip side, of course, is that they themselves won't ever use cheap gear, so it's basically a veiled way of saying "hey kiddie, go play with your cheap toys and leave us serious folks shovel all the coin off recording". So the SM57 is a favourite of serious studios because they have the sort of expensive gear (and money) that affords them to fling a couple hundred spare change on mediocre microphones like SM57.
Still, if you've chipped in and are stuck with the SM57, by now you should be well aware that it won't ever give you the kind of sound big studios get with it. Unless, that is, you bother fixing it.
There's a couple mods that fix the two SM57 defects, low impedance, and the (sometimes honky) elevated midrange/treble.
The trouble with SM57's low impedance is, its diaphragm wobbles. Low impedance makes the high midrange/treble unstable, so basically the thing loses valuable space/harmonic shape definition. Which is why it sounds harsh. Low impedance simply allows the diaphragm to overshoot and vibrate too much at high frequencies - it only gets relatively stable at lower frequencies. The same is true for headphones, by the way - high-impedance headphones are always more stable and precise. So the fix is simply an adapter cable with a resistor in it. The original design features a resistor of 698 ohm for matching with a professional preamp. However, just about anything around 600-700 ohm will do, or a different value, adjusted for a specific preamp. In the original design, the resistor is simply soldered between pin 2 and 3 connections inside the male XLR plug (the cable's just a short male->female XLR affair). The resistor can also be soldered directly in the microphone's XLR socket. Just remove the release screw in the bottom of the SM57, and pull the XLR socket with pliers, then solder the resistor inside the socket between pins 2 and 3 (not on the working side, obviously).
An impedance adapter. It works wonders for other low-impedance microphones, by the way. It's this fat because of a huge 1-inch industrial copper braid used for shielding.
Transformer removal is just that. The transformer is responsible for some of SM57's slowness and, yes, the dreaded high midrange/treble honk. The only downside is, the SM57 will become even less efficient with the transformer removed; it loses about 12 dB of loudness. Removing the transformer may not be such a good idea if all you've got is a weakish sound interface or mixer for preamps.
Anyway, the transformer is hot-glued. All you have to do is boil the thing for a while (not until the paint peels off, though that's a matter of choice, as the depolished microphone could be painted in a different colour or just stay that way for easy recognition). The glue will then melt, and the thing has to be pulled out, again, with pliers.
That ought to fix the sound, making it rather more mellow/natural, and thus sparing some EQ work.
For those who use the thing transformerless, an EQ won't readily fix the slightly boxy/woolly dynamics, but here's an EQ preset for Spline EQ which is an inverted frequency response of the SM57.