okay, in case anybody cares, I bought my mic yesterday. I went into a place and I ended up talking to the store manager (I didn't know this until after I had been talking to him for a while)... He was really nice and knew what he was talking about. He explained all the different specs to me and what was good and what was bad, and let me try all the different mics I was interested in in a sound booth (unbelieveably helpful).
I ended up buying an Audix OM-5. It has a 48Hz - 19Khz freq range, really low impedance, and gold-plated contacts. I got a great deal, they threw in a 20ft monster cable. I took it to reheasal last night and it sounds wonderful!
Thanks to you all for your great suggestions... I did try the SM-58, which so many of you recommended, but found that for my voice, the Audix sounded better. However, I'm going to recommend the SM-58 to a friend whose voice is, I think, better suited to that mic.

Thanks again!

-Branwen-