[jimmy]

I'm guessing you are using the camera in fully manual mode with the nikon lens ?
I like the last shot most but all your shots look a bit underexposed to me, even just a bit of post processing in photoshop would make them look nicer.
It might be an idea especially if you are in fully Manual mode to take a couple of shots and have a look at the histograms, the photos you posted are all shifted over to the left, they should be more evenly spread if the photo is exposed correctly.
Not sure how you do it on your canon but you will be able to see the histogram of any photo after you have taken it.

having said that, if F5.6 is the biggest aperture available then you would have to slow the shutter speed to get more light in which could result in less "keepers". You can lighten the photos afterwards in photoshop but this can make them noisy.

The 20d seems to do a really good job at iso3200, are these photos full frame or cropped ?