The blade sharpener that I almost forgot about is a ruler with a honing thingy in it.
I have this one and it is not for sharpening a dull blade but to keep a sharp blade sharp. It works great. I run my blade in it a every so often when cutting. The secret to keeping a sharp blade is to sharpen a sharp blade. Like cleaning a clean house, it never gets dirty.
http://www.sewforless.com/item/Grace...FVE8gQodCKQFdw