I have an external mic with headphones. The headsets are usually sacrifice a lot in sound quality so if you want to listen music as well, it's best to buy good headphones instead.
The mic choice is a lot trickier, since they are either these $10 microphones or the $150 ones...
At the moment I'm using Sony MDR-CD580 as headphones and my webcam (Logitech QuickCam Fusion) as a microphone. The mic quality isn't too good, but it's sufficient.
But anyway, if it's only for gaming, headsets are probably your best bet. I don't exactly agree with Stonewall, if you buy poor headsets, you'll get annoyed at the sound quality. $50 should get you a decent one though, I guess.
A word of warning though, no matter how much money you put into audio, you'll always find better quality.
I'd say this is slightly off-topic though, so I'm marking it as such.
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