Wouldn't worry about it mate, most anything will work just fine. Audio compression over the Internet makes the audio quality fairly low anyway. So any mic/headset will no doubt be fine.
I would buy one with a long cable, volume control and mic on/off switch on by the headset on the cable.
Very good, not expensive! If you dont get 1 of these 1 make sure the Mic is long enough to reach your mouth and is moveable (like the 2 posted) otherwise people wont be able to hear you very well!
I know this because of the last pair i had were crap!