Need Mic for World of Warcraft - iSight a good choice?

I need to pick up a microphone to use for when I'm playing World of Warcraft. The built-in mic doesn't cut it, since WoW causes my iMac to run rather loudly, and the mic picks up all the noise. I was looking at getting an external iSight to use, both as a microphone for playing WoW, and for video conferencing, etc. I just don't know how well the mic works. Will it pick up the same fan noise, etc, being located on top of the screen?

 

I use my iPod headphones a lot, so any kind of echo wouldn't be a problem.

 

If I did get a separate mic, is USB the best option with the iMac?