Fastenal also has some nice little (~4"x6") card size decimal/drill/tap charts that they give away for free. They are right on the checkout counter at our local store. We usually stick one in the various boxes of drill bits. Fastenal also has a nice wall chart of different types of nuts, bolts, screws, etc. showing all the different head types and grades, etc. that is pretty handy to have hanging in the shop as well. I think they are also free. I looked around on the Fastenal website to see if they have them available as a PDF but I didn't see them. I did find this pretty handy PDF reference guide though:
http://www.fastenal.com/content/docu...renceGuide.pdf