I use 2 Gopro HD2's for filming mainly in open spaces, where I get a lot of wind noise, and I have to say the sound quality is pretty bad on the standard camera, I normally have to take the sound out and add music in post production. After a bit of research the Polar Pro microphones seemed the best value for money and the video's on youtube seemed to show them in a positive light.
I ordered two Polar Pro's which were delivered very quickly. On opening the package the microphones did not look up to much, squashed in small plastic packets and looked quite cheap. Once opened and fluffed up both mic's looked more like the pictures I'd seen. With a little care they should last a long time.
I first tested them on quite a strong wind day in a wide open space, and I have to say these Mic's are Brilliant !!! They take away 90% of all the wind noise, but all the sound you want is still there, they also seem to sharpen up peoples voices to give a fantastic difference to your video's, I also tried them inside and they make a big difference to the standard camera microphone.
I highly recommend these microphones.