First off, I'm not expert on microphones, but I suspect that the experts would tell you it depends on your needs (Stereo, Shotgun, etc.). It's important to get a good microphone, but even a good microphone does a poor job, if you can't get close.
I currently have a "Rode SVM Stereo Condenser Microphone". I get clear sound and am very happy with it on my 60D. It's far better than the build in mic, especially if there is any wind. Since it's stereo it picks up nice ambiance, such as ocean waves, crowd noise, etc., but it doesn't do as good of job for dialog. I'm considering purchasing the "Rode VideoMic Pro VMP Shotgun Microphone", for dialog. Even with a shotgun microphone you still need to be no more than a few feet away from the subject. I'm also considering the purchase of a wireless kit and lavalier microphone, for times that I can't get close.
One thing I would really like to see, would be a head phone jack on the camera for monitoring audio. I've been looking for an add-on solution, but haven't decided on anything, yet.