Route 66 Riders
Where I rented.

Road Trip USA
Very useful book (and website) with a selection of routes using America's quieter and more interesting roads

The Art of Travel, Alain de Botton
Started reading this just before going. Worth doing.

Jupiter's Travels Ted Simon
Read this years ago, been to website and feel due for re-read.

Zen and the Art of Motorcycle Maintenance, Robert M Pirsig
Another one from many years ago, and took it on the trip to re-read. If you want to get a long way off motorcycle touring, he hosts a discussion list.

Motorcycle Touring For Beginners

Doc's Motorcycle Touring Pit Stop

Horizons Unlimited

Lois on the Loose
Someone I met on Route 66 told me about her. Her route is one I have always wanted to do.

Adventure Motorcycling
Some more ideas

Bike history:
Previously, longest touring had been about 1800 miles round Ireland in 1981. Three of us, on Honda C70 and 90s.
Over the years have owned: Norton Jubilee, Matchless G5, Triumph Bonneville T120, Honda C70, BMW R60/5, BMW R80/7, several Honda C90s, AJS Model 20, Honda Revere NTV600, BMW R850R. Of all, my greatest fondness is for the Matchless, YOY997, which sat for many years as a prospective restoration project, before being sold.