Check this out, want to bring a little organisation to your Dock? Add spacers with this command:

defaults write com.apple.dock persistent-apps -array-add '{"tile-type"="spacer-tile";}'

Do this as many times as you want spacers then restart the Dock

killall Dock

Move the spacers around like any other Dock icon, menu click or drag off to remove them. Easy!

Got it here: http://www.flickr.com/photos/hetima/1839756788/