I've heard some people speak well of the AT2020 USB but the other one you may wish to look at would be the Blue Yeti which also sounds very good and should be well within your price range.
However, I have to ask what things you want to record? If you just want to record a podcast or audiobook and will only ever need one mic, then a USB mic might be for you. However, if you're planning to start recording music, I'd strongly suggest you up your budget slightly and get a USB audio interface and an XLR microphone.
Why? First, the monitoring options on most USB mics are useless. On most of them you have to use the built in sound card on your computer to feed your headphones--which means a round trip via your computer and lots of latency. Even most basic USB interfaces have "direct hardware monitoring" which allows you to listen to a mix of what you're recording and backing tracks on the computer. It'll also use ASIO drivers which are hugely superior for any serious recording. Finally, a USB mic is a dead end if you ever decide you want to add a second mic or even just a different mic for different source material.