Brent Beach has an article in FineWoodworking #184 about sharpening planes and chisels with sandpaper. I’ve been doing this for a while, with mixed results.
The article had some tips I’m going to try, and also a link to Brent’s website for more information.
And man, is there more information. Tons of information. More than you’d ever need to know about sharpening.
It’s a great resource.