With monopods you have to consider a few things that have to match up; weight of camera, style of head, maximum length, weight of monopod and head together.
I have a standard Manfrotto monopod with an inexpensive standard style and standard size ball head, and I take the monopod around easily. It really helps many shots. If I can then find something to lean the monopod against other than myself, I then have the two points of solid contact in addition to my holding the camera. This allows a major improvement in stability with such little weight and inconvenience!
The trick is to shop around for something with strength and solid construction but with the least weight. The new metals and designs are bringing down monopod and tripod weights quite a bit. I also think that a good ball head with a removeable plate that attaches to the camera is the only way to go. You want to be able to remove the camera and reattach it to the monopod very quickly and easily as often as you change yourmind about what to take photos of.
I find that the standard issue ball heads from Manfrotto and premium tripod companies are very expensive and overly large for smaller cameras. Less expensive, but well built heads are commonly available.