I love using my KIRK MPA-1 swivel head on my monopod. This is a Manfrotto 234 (previously the 3232) tilt head with a KIRK Arca Compatible quick release clamp added.
Really Right Stuff also distributes an Arca Compatible monopod tilt head based on the Manfrotto 234 which I would assume is equally as good as the KIRK MPA-1.
Since, I do not normally use anything heavier than my 40D camera with 70-200mm f/4L IS lens on my lightweight (Calumet) monopod, the MPA-1 is a good option.
If I were going to use a heavier combination, I would select the RRS "High Capacity Monopod Solution" which is a heavy duty option but, which is quite a bit more expensive than the MPA-1. I would also use a more heavy duty monopod.
I generally carry two cameras: a 40D with the 70-200mm f/4L IS lens and the 30D with the 17-55mm f/2.8 IS lens. I have a RRS L-plate for the 30D and a generic Arca Compatible plate for the tripod ring of the 70-200mm lens. It is very easy to switch cameras using this setup. I enjoy using a monopod because even with IS assistance, I will often encounter shots in light levels low enough to make hand holding difficult. The Calumet monopod that I use weighs only .95 pounds. When I don't need the pod, I sling it across my back using a strap.
I also have a Manfrotto monopod belt pouch which can add stability to a shot when placing the monopod on the ground is not an option. This is especially good on boats which have engine vibrations which can be transmitted even through a graphite monopod.
Additionally, the RRS L-plate allows me to position my 30D with the 17-55mm lens in the vertical position without having to cantilever my camera over to the side. This makes a lot more solid support since the monopod is directly beneath the camera when I am in the vertical portrait position.
I have re-oriented the KIRK quick release plate so that when I am shooting, the channel is oriented parallel to the width of the camera rather than perpendicular to the camera body. This allows the head to tilt up and down. In the OEM orientation with the channel at 90 degrees to the width of the camera, the tilt of the MPA-1 will only go side to side when a camera is mounted using the RRS L-plate. I prefer my tilt to go up and down. It is a simple two minute procedure will an Allen wrench to reorient the quick release.