I second the motion for a monopod.
It is light, and gives all the support you might need for even your longest lens.
It is also acceptable in some places where a tripod would be banned.
I would suggest a tilt - not pan - head for it for maximum flexibility.
Mickey
I posted this in March 2011.
You don't need a rotating (pan) head on a monpod. The pod and camera rotate together on the ground as one unit.
You do need a tilt only head, however to increase the stability and versatility of the monopod.
The one shown in the picture is a Manfrotto 234 Tilt head. It is solid, well built, easy to adjust and use for left or right hand use. About $30.
Vistek has a good selection.
Lee Valley listing under Garden Supplies - Telescopic hiking sticks is my by now well used monopod. Notice the height of the monopod. It can be extended even more.
Try this. Unless you are short, I would suggest the longer one.
http://www.leevalley.com/en/garden/page.aspx?p=52925&cat=2,40725,45454,52925
A quick release as small and as flat as possible will increase the friendliness of your monopod.
Mickey