My 5x24 inch ruler. I use it for tons of things and it fits just right on my table. I have a couple of the green shaded rulers, and I can't see through them, I'm going to have to stick with black/white from now on.
I also love the flat daisy pins, they are just right for matching seams, not too thick to distort things and easy to pull out as I sew.
And I love my Janome 6600! It is a great machine~!