What hardware is needed to record a podcast using the new Macbook Air?

I'm interested in the new Macbook Air but it has no audio input only USB. I currently own an Intel iMac and record my podcasts using a Shure SM7B connected to a Presonus TubePre mic preamp and then into the audio input of my iMac. My voice sounds excellent recording with this setup. What hardware (be specific) do I need in order to record using the Macbook Air's USB port. I owned a USB mic once and wasn't happy with the quality of the output. And I definitely do not want to use the internal mic. So with my existing mic and preamp what hardware do I need to input audio into the Macbook Air? Thanks.