I have a few that I like:
DMT Mini-sharp [~$11.00] (Specifically the Blue, and sometimes Red, one of these.)
Smith's DRET [~$7.00] (Gerber also has a version that seems to be exactly the same, but in silver and black)
(^note: This is one sharpener, but it has two sides. The pointy end and the rounded end.^)
Smith's PP1 [~$12.00]
The DMT seems to put the best edge on my plain edge blades, but the other two provide a perfectly serviceable edge and will also sharpen serrated blades, which is a nice touch. I have a few DRETs stashed throughout my gear because they're cheap, easy to get (walmart), and it's very versatile.
The only thing I don't like about them is over time they do wear out (I guess all the diamond dust comes off), but they do last for a very long time. However, I guess if I was planning on spending a few years out in the bush I think I might rather have a simple old-fashioned "Arkansas Stone." They don't work as fast as the diamond stones/rods, but they do seem to last longer.