For the money the SM57 does a good job on miking amps for recording.
SM-58 good for Live Vocals, but don't try and record with it.. You need a condensor Mic for that.
I had a cheap marshal mic that sounded great.
Lots of albums done with SM58 on lead vox or a Shure SM7 (note SM7, not SM57 there) which is also a dynamic... Michael Jackson, Pearl Jam, U2 and the list goes on. In fact both of these mics are the two most recommended by recording engineers to home studio guys who might not have the best sounding room to record in and want to reject as much of the sound of the room as possible.
You absolutely don't "need" a condenser and in fact it's not always the best weapon of choice for a particular singer or tracking situation.
I know personally of a particular album by a popular Canadian band in the late 80's where an SM58 was used for lead vox because the singer needed to run around and do his "live" thing to catch a great vocal performance and couldn't stand still in front of a mounted condenser to save his life... and this is actually quite common in a studio environment, more than you think.
An SM7 (SM7A SM7B) is used quite extensively on female vocals in the studio.
Anyway, just wanted to point out that needing a condenser to record a totally pro sounding vocal track is as much a myth as needing for that condenser to be a tube mic... you just need a good mic... period (and that does include the SM57, SM58 and certain other dynamics that aren't high dollar mics relatively speaking)... oh, yeah, and a good singer (wink).
Now using a good mic pre is a whole different ball game. A SM58 into a high end pre is not the same as an SM58 into some crappy 60 dollar entry level pre or the channel pres in some mixer or cheap interfaces and/or converters... but neither is a condenser.
By the way, yes there are some Marshall (as well as some other Chinese made) mics that do sound decent and some of them are even rather stellar once modded.
An even better bet are the rather decently priced Russian made Oktava mics which also are great sounding mics to begin with (blow the Chinese mics out of the water) and once modded (by Michael Joly of oktavamod.com for instance or there are DIY kits) are on par with some of the most desired mics out there. I bought two Oktava MK-319 mics off ebay for a little over 100 bucks each... they are getting modded by Mr. Joly this summer. He also mods other mics including some of those Marshalls
The Oktava small diaphragms like the MK-012 (aka MC-012) are great on acoustic guitar and drum overheads... and once modded are even better, and will give even Neumanns a run for their money.