I went looking for a USB headset microphone, and the Telex H-841 USB Digital Computer Headset seems to be the cheapest one that doesn’t suck. Amazon’s users comments for the other headsets in that price range (under 50 bucks) spoke of bad sound, uncomfortable fit, and fragile parts. The customer reviews of the Telex H-841, on the other hand, all rate it 5 out of 5 and commend its quality.
I’ll have to check it out.