I'm having trouble recording a decent sound from my snare. The snare itself sounds OK, but once it is recorded it sounds muffled and really bland.
First things first: The snare sounds OK on it's own. Make the snare sound killer on it's own. If you start with a killer snare and make an extraordinary mess of the recording, you probably will end up with at least an OK snare. But we're not going to make an extraordinary mess of the recording.

Seriously, I spend at least an hour auditioning different snares, tuning, muffling, moving the whole kit around the room, before I even think about picking up a microphone. And this is after years of learning how to get the sound I want. Expect to spend much longer.
I have experimented with different mic distances to negate the proximity effect, but it seems that I have to move the snare further than I would like to get the mud to go away. (To the point where the snare is not isolated at all and I'm getting too much of the rest of the kit.)
Isolation is overrated. If your sound is better with bleed, go with the bleed. Monitor in real time (as far away from the kit as you can get your speakers) as somebody else moves mics around slowly.
I have tried cutting the lows down a lot, but the result was a muffled snare with no punch - even worse! I have used an sm-57 and an akg 1000 and both seem to give similar results.
If you have to use EQ to make a mic input acceptable, back up because something is wrong. But if you spent the time described above to make your sound killer in the room, you are probably not having this problem right now.
I have heard many live shows where someone just clipped a sm57 to the snare, two inches from the head and it sounded good.
At a live show you are hearing a ton of sound coming off the snare itself or bleeding through the singer's mic. Use a room mic in addition to your overheads to get this on a recording. If you don't have enough tracks/inputs/mics, ditch the overheads before you ditch the room mic. Hell, ditch the snare mic before you ditch the room mic. Except for the exceptions, of course.
I'm not looking for a dynamite sound here, (though I'll take it if I ever get it!) just something good that will pass the smell test.
Anyway, at the end of the day everything I wrote is secondary. If you put Billy Martain or John Fishman on a $30 junker kit in a crap room you still probably couldn't screw up the recording if you tried. The guy doing the actual pounding is how you get the snare at the right volume ringing with a nice tone and cutting through the cymbals.