Building a good road books is something quite complicated...Here could you find some inspiration.
Absolutely necessary for a good plan. Most of the them are well detailed, and indicate touristic points of interest. I especailly like the Michelin ones (1/200 000 for France, national ones for other countries).
Internet gave me the key ideas for most of my trips. Just search other riders sites, I 'm sure the way they like travelling is close from yours. To find these sites, I have no miracle solution...search engine and let's go !! Here are some sites I especially like : nomadd, chtimotardes and horizonsunlimited . Be careful, last one is for ambitious riders, who want to travel in Siberia or Patagonia. But it's full of good tips, it's really worth visiting it !!
Give the additional information you couldn't find before : touristic and cultural overview, practical tips...According to your wishes, you can buy lonely planet, Michelin guides...better is to go to bookshop to do your shopping.
I'm sure some motorcycling magazines of your country do special tourism editions, with road books indications.
Hey, it's its purpose !!