This is a mic that has worked really well for our users. Not the prettiest but the audio is solid: http://www.amazon.com/Samson-Mic-Compact-USB-Microphone/dp/B...

I have had almost 100% success with the mic built into my laptop (macbook pro 2010). The ONLY issue I've ever had was it sometimes can't pick up a low open E. But very rare.