I used a RRS L bracket on a Canon Rebel for a while. The nice thing is that the lens stays centered on the same view unlike using the flip feature of a ball-head which requires re-orienting the camera
Jay,
If you are getting the sidekick, it does the same thing (getting the camera to portrait mode) and would be less weight to carry than the sidekick plus an L-bracket.
Thanks Roger, sidekick arrived today. I will set up the sidekick with my 40D; my brain is not imaging the camera in portrait mode with the sidekick. Cheers, Jay