yeah, I just went and bought one of those crappy GE one's from target that're meant for receptionists. Works well enough for $20 I'd say.
If you're lookin for a really good set, go with some Plantronics or something. They're nice, but rather spendy.
As far as the noise with a stand alone mic, you can crank down the input level for the mic so it doesn't detect as much, but then you're gonna have to talk louder for anyone to hear ya.
Overall, I'd say just grab a headset. That way ppl on the other end don't hear a half second lag from the sound comin out of your speakers goin through your mic and bein played back at them through CS.