Over at Ramshackle Solid, Eric recommeds a pull-cord powered, double-edge razor blade sharpener. I didn't even know that anyone was still making double-edge razor blades!
You just clip your used blade onto the pegs, close the lid and pull the cord a few times. The cord spins the pegs in little orbits which passes both sides of the blade over the interlocking sharpening element which has the right angle to sharpen the blade back to good as new condition.
I used it for the first time this morning and the blade felt brand new.
Razor blade sharpener