I have had several clients ask me what microphone I would recommend for shooting videos. I've got a couple, but the Audio Technica Twin Wireless Microphone System has been my favorite. It is reasonably priced, wireless so I can move around, and has great sound. I bought mine on Amazon.com
which is where I found the best price.
If you'd like to check out the other microphones I've used, check out this blog.
Here is a video I shot with this microphone.