The Audio Technica ATR2100 USB is a USB and XLR mic that features a dynamic capsule to reject background noise
Though they don't make these anymore, these are highly affordable and produce very good sound quality for the price. Great on the go recording as well, if you are using your computer with USB.
I use this TweetRemote co-host uses this and sounds great. Plugged right into his mac via USB connection, no issues. He also monitors himself from the output on the mic. I'm very impressed, though I heard Audio Technica has since discontinued the ATR2100.
I use this Tweet