Originally Posted by portishead
From your post it looks like you are looking in the $100 range.
An SM58 is probably your best choice for that. Record your vox with it, remove the ball on the mic (it unscrews and comes right off) and record your acoustic guitar. Done and done.
or a 57 with a proper circular separately mounted pop filter and/or a foam overthemic filter.
For your budget and dynamic requirements just use the industry standards. they're standards for good reasons. you have few options.
other dynamics that are good but may sound different are from
heil (they TEND to be brighter and more condensor-sounding than shures, as a really general guideline),
audix (the om2 is a great and affordable mic, it's got a presence peak that is imho stronger than that of the shure competitors which makes it great on some things, lousy on others, and there are other om models in their line up with different sounds and prices).
peavey (but hard to find now) like my old favorite pvm 520 dynamic. it's similar to an re 20 and can be found used for like $100ish if you're lucky enough to find one and the seller isn't trying to rip you off.
and of course there are various knock of dynamics that are also quite good :
apex make surprisingly good sounding sm58 knock offs if you get the right model numbers and they're about half price of the real things. not quite the same but in the ballpark, sound wise.