Here's a great lens to go with your Canon dSLR to shoot the moon. It's got 1,200mm of focal length as well as a relatively fast f stop of 5.6.
This should just about fill up the frame with a Canon crop sensor (APS-C) camera such as my Canon 30D. With the crop factor of 1.6x, the lens becomes a 1,920mm lens. My Coulter is roughly 2,400mm with my 30D and can barely fit the moon in on one frame.
The price is a bit high, but for those with the money, it's well worth it!
Here's the B&H video of it on an outing.