A few weeks ago, a good friend of mine introduced me to an iPad/iPhone app called Motion Math Zoom. This game is a highly visual, intuitive exploration of the number line. With help from cute animal pictures, the player gets a good sense of scale when looking at pieces of the line, marked off by ones, tens, hundreds, thousands, thousandths, hundredths, and tenths. The scale can be changed with a simple finger pinch.
I was impressed with this game, and a little sad that it didn't include fractions in fraction form. So one day, needing the kids to have something to do while I cooked dinner, I used masking tape to mark off a number line along the tiles on our kitchen/dining room floor.