The bigger factor in my mind is actually the tripod head that holds the camera to the tripod, allows you to angle it, swivel it and potentially pan. Note that they are actually heavier than the tripod. I tested a few from www.borrowlenses.com prior to making a decision.
if you want a lo-fi version you could attach string to a pencil, find a hook/screw that fits in your tripod mount, stand on said pencil, meaure the length to where you hold the camera up to your eye and tie the string to the hook or make a quick disconnect. Keep it in your pocket for when you need a steady shot. Not as good as a real monopod but handy and compact.
I have two monpods, a Manfroto 680B and a Vanguard Tracker II. Both have good points and some cautions. The Manfroto is sturdy and stable. The Vanguard is lighter and seems less stable. I use the Vanguard 250 ballhead on both and find it to be great and easy to control.
Cool tip: In wintertime, or on soft, yielding surfaces, I use a plastic skiing pole basket, that can be mounted on the end of the monopod, to give it better support, so it won't sink in.
@mabuss - Check out your local sporting goods stores, especially those that specialize in hiking equipment. I have a Komperdell hiking staff that is also a monopod. There is a cork knob at the top that unscrews and you can screw your camera onto the top of the staff where the cork knob was.
Height is adjustable and it has anti-shock built in as well.
@mabuss I have a VersaPod which is much like the Trekpod that Aaron @grizzlysghost mentioned above and i use it all the time. I really like the versatility of it kicking out the feet when a tripod would be handy (only on a flat surface mind you and with a remote trigger). It works well as a walking staff as well and has a really strong magnet for quick on/off of my 60D. Now, when using the tripod function it is fairly unstable which why the remote trigger is needed, but that is the only real issue that I have experienced. Good luck!
The bigger factor in my mind is actually the tripod head that holds the camera to the tripod, allows you to angle it, swivel it and potentially pan. Note that they are actually heavier than the tripod. I tested a few from www.borrowlenses.com prior to making a decision.
http://www.manfrotto.com/294-aluminum-monopod-4-sections
I use the 496RC2 head.
http://www.manfrotto.com/compact-ball-head-with-rc2
tagging @jay_fuller for good taste ;)
Cool tip: In wintertime, or on soft, yielding surfaces, I use a plastic skiing pole basket, that can be mounted on the end of the monopod, to give it better support, so it won't sink in.
Height is adjustable and it has anti-shock built in as well.