Here's a stand-alone mic (not a headphone/mic combo) that should work: I just ordered one - for $1.44+free shipping I don't think you can go wrong:
http://www.amazon.com/gp/product/B00...=5336653508-20
The type of plug needed is called a TRRS plug - it has four conductors on it, rather than the three conductors found on the (TRS) plug on normal stereo headphones. If the plug has three "stripes" on it, it's a TRRS.