After listening to Les Stroud tell us how he never goes anywhere without "a good multi-tool"; I decided I probably should pick one up. I got to looking at a few brands, mainley the Gerber and the Leatherman's. After narrowing it down to a few models, I decieded to go with the Leatherman "Blast". It seemed to be the best blend of features (that I would need) vs. weight. At 6.9 Oz, it has most of the stuff I think you would need, and is 2oz less than the "Wave", and 5oz less than the "Surge".
I have been wearing it on my off hip and I forget it's even there.

What Multi-tools are you guys wearing / using?
Here's a pic of the "Blast"