These are currently the top 10 best-selling USB microphones at Guitar Center.

1. MXL MXL 990 USB Powered Condenser Microphone
2. Nady USB-24M USB Microphone
3. Blue Snowflake USB Microphone
4. Nady USB-1CMS USB Condenser Microphone with Sony Acid Music Studio
5. MXL USB.008 Large Gold Diaphragm USB Condenser
6. Nady USB-1C USB Condenser Microphone
7. Blue Eyeball USB Microphone with Webcam
8. MXL USB.009 24/96 Digital USB Condenser
9. MXL 990 USB Stereo Condenser Microphone
10. Rode Microphones Podcaster USB Microphone

Check out the Best Selling Musical Instruments Archive.
Search for USB Microphones on eBay.