One of the more common questions I get these days is about how to record good quality audio when using Canon dSLRs to record video. I have several recommendations on this, and it isn't a quick answer, most of it depends on what you are doing, how many people are involved, and the location of the shoot.
For starters, the microphones that are built into dSLR cameras as of today are pretty much worthless. They are "Omni-Directional" meaning they record sounds from all directions equally. What this means is when you pick up the camera, activate focus, breathe too hard on it, all these sounds are recorded onto the file. It is annoying and impossible to get good quality audio with the built in mic. Your sound quality is only as good at the type of microphone you are using, as well as its "recording pattern".
The first microphone I would recommend is a RODE dSLR mic. There are several offerings right now, I like the Pro version because it is more compact: RODE Pro Compact dSLR Microphone
and there is also an entry level microphone which is also highly rated: Entry Level RODE dSLR Microphone
. An important note; if your video camera has a microphone input (most do) you should be able to use it- even if it isn't a dSLR, but rather a compact dedicated video camera.
These microphones are different in that they record in a "directional pattern" which means that they record audio from one specific direction better than others, which means better audio quality. These RODE Mics also have built in suspension bands which allow the microphone to "flex" on its mount, this also leads to better audio quality.
All this said…these are good microphones, much better than the on board mic, and will work for most people. They are not however… what I would consider "pro grade", ie something used for making a movie, high quality interview, training dvd or anything else for high end type work.
In any event, if you have a video camera with mic input and are not happy with the quality of your audio, this is a good place to start:
RODE Pro Compact dSLR Microphone
Entry Level RODE dSLR Microphone
More to come on Mics!