The H4N is the way to go if you have the money for it. If you're looking for something a bit cheeper, I would go with the Rode VideoMic Pro or the cheaper Rode VideoMic. I currently have the VideoMic Pro and couldn't be happier with it.
Get this instead:
http://www.amazon.com/Rode-VideoMic-VMP-Shotgun-Microphone/dp/B004K8WPUQ
go for the preamped one, plus the built is ergonomically better. I have the Rode VideoMic and the shock mount is suspended by those rubber bands. The rubber band caused a break in the mount, where the tabs are.