Dock Spacers

Get a blank icon, and put it on the dock.

 

If you go here, and then go about two/thirds of the way down the page, there is a section called "Dock Dividers." Download the appropriate one (horizontal or vertical) and then unstuff it. Inside the resulting folder, there is one called "Blank.app." Replace the name of this with a space (leaving the extension .app), and then duplicate it as many times as you need it to appear in the Dock, giving it one more space in it's name every time. When you have enough, drag 'em down to the Dock wherever you want them. Tada! Blank Dock Dividers!