What is a good microphone for sound/voice recording?

I'm looking for good/great mics to record voice for commentaries. I currently have the tritton ax 720 headset for the xbox with a pc plug in and am wondering if that'll be good enough or not. Also what would be some recommended audio recording software for my cpu? Preferably free/ cheap and would Sony Vegas pro 8-10 be sufficient? Thank you very much for the help! :)