57s are a standard on guitar amps but not usually by themselves (in a studio situation)... usually paired with a large diaphragm condenser (watch out for phase issues... putting 2 mics on a guitar amp is more of an art than a lot of people realize, if you are new to recording you'll probably get better results from a single mic). I'm leaning more towards the Sennheiser 421 these days for guitar amps.
As great a mic a Shure 57 is, if you want "that commercial" sound on your vocal recordings even a cheap large diaphragm condenser will do the vocal more justice.
Someone was asking about a good general all purpose mic...
I can't say enough about a mic that is sort of a little known dirty little secret... the M-Audio Solaris, a $300 large diaphragm condenser. I'm pretty finicky when it comes to home recording and getting "that commercial cd' sound and it takes alot to impress me when I'm listening to clips online that people have posted. I was in another forum and heard a guys tune where the quality of the vocal recording just floored me, and I don't just mean his performance. I contacted him to ask what he used expecting him to tell me it was a U87 or something and he said it was the Solaris... no preamp or post processing other than a tiny bit of verb and delay and some compression. I went out and bought one the next day. It's now my goto mic for everything from a second amp mic to vocals and anything in between if needed... and it has all the features of more expensive condensers - pad, 3 patterns, low pass and its own spider mount and case.