There’s nothing like a bit of content poaching, but I came across this particular thing over in the Brickset forums.
Tom Alphin is clearly no stranger to dealing with numerous LEGO parts, so much so that he took matters into his own hands and created a printable LEGO ruler and sorting tool. He’s even been generous enough to share it, and you can find a link to it on his weblog post.
I’ve literally just come across the post now so I haven’t been able to give it a try – however I can already see it’s going to be incredibly useful. It may be worth printing a few just in case, perhaps even having a laminated copy.