The link in the previous message has changed significantly since the last time I used it (a long time ago). It no longer produces an output file of waypoints. It just produces a map with the waypoints flagged on it. Neat but not useful for this purpose.
I found a different link that's still pretty easy to use: www.findlatitudeandlongitude.com/batch-geocode/#.VqAMJiorK70
You cut/paste the address, city, state columns into the "Input" box, select the options you want for the output and poke the "Geocode" button. It will produce a list of the coordinates in the "Output" box.
The easiest way to use this site is to use the default settings.
Select the data in the address, city, state columns in your spreadsheet. Do NOT select the headers in the columns, just the data under them. Paste it into the "Input" box.
Click the "Geocode" button. Watch the counter in the upper left box as the geocoding is done.
Select all of the data in the "Output" box (click in the box and hit Ctrl-A).
Open your favorite text editor and paste the data into it. Save it as a .CSV file.
I took a look at Google Earth and I cannot find any simple way to create routes with multiple waypoints in them.
So you need to convert the .CSV file with your waypoints to something you can use in Basecamp. You can do this using the GPS Visualizer web site: http://www.gpsvisualizer.com/gpsbabel/
Select "Universal csv with field structures in first line..." as the Input file type.
Select "GPX XML" as the Output file type.
Select your CSV file and click the Convert button.
When the conversion is done, click the resulting link to download the .GPX file.
Open Basecamp and import the file into a list.
In Basecamp select all of the waypoints in the list (click in the list and type Ctrl-A). Right-click in the list and select "Create route using selected waypoints".
After the route is calculated it will likely look like a bowl of spaghetti. Click on the "Unlisted Data" item to see the route. Right-click on the route name and select "Optimize route. It will ask you if you want to keep the last address in the list as the final point in the route. You can say "Yes" or you can say "No" and change it.
The optimized route should look a lot less spaghetti in the bowl.
One of the things that's rather handy in Basecamp is that you can display the waypoints on the map without creating a route. Using the selection pointer you can drag a box around a group of waypoints that are located near each other, right-click on one of the waypoints in the list, select to create a route with the selected waypoints and then optimize the created route. This is probably the easiest way to create multiple routes from a big list.
I know that's a lot to take in but since I can't just pop over for tea it's the best I can do. You'll have to do some experimenting yourself.