A new feature from Google Maps will help you plan your next roadtrip:
The core Google Maps service has improved its directions feature by allowing you to enter more than 2 locations to plot directions between. Now when you plot directions between 2 points a link appears at the bottom of the instructions to the left labeled "Add Destination".
Click this link to enter more places to add to your route plotting. It doesn't appear to have a limit for the number of locations you can add and it will also auto-complete places from your 'Saved Locations' area if you have this feature enabled. This looks to be active for most Google Maps countries: USA, Canada, UK & Ireland, Japan, Germany, Spain, France and Italy. Perhaps the next feature addition will help NASA plot directions from Earth, the Moon.. then Mars! :)