Submitted by Matt
Another product I constantly use for keepin knives sharp is the Diafold by DMT. It is a diamond impregnated steel mesh mounted to a plastic plate. It has handles that fold around it like a butterfly knife. Comes in multiple grits. Weights about 1.5 oz. Very handy and effective, lasts a very long time. I've always used mine dry, and get around 10 years of use out of them. They are handy enough to carry in a pocket or tuck into a tool pouch etc. I use the blue, medium grit for sharpening everything.
ED -- Matt, funny you should bring up DMT. My first sharpener was a 6" DMT bench whetstone (blue, med. grit.) Unfortunately as soon as my mother found out about it she decided it was just the thing for her kitchen knives so I always ended having to wait in line behind her.
In addition to the standard rectangular stone, DMT offers Diafolds for serrated blades, fishooks, pruners and shears, and chainsaw chain as well as double sided stones (combination grits.)