Check out this site: http://www.boltdepot.com/fastener-information/Measuring/TPIandPitch.aspx
The site talks about thread count and pitch and has some useful charts. What I like best however is the printable PDF thread gauge. There are a variety of tools that I think it is nice to have around the shop for information like a drill index guide (so your bits always get returned to the right spot), and this guide, printed (and maybe even laminated!) needs to join the ranks.
By the way, Bolt Depot, the site where the threat gauge is at also has a variety of other printable PDF's. http://www.boltdepot.com/fastener-information/Printable-Tools/Default.aspx Will get you to that site.
Also, at the same site is a chart describing metric us grading. http://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx
In short, the Bolt Depot definitely cuts it as site of the day.