I find Google maps invaluable for checking towns - though Google maps is just as good, I suppose. The hotel links and photos of places lets you see what it looks like and a good idea about shops and accommodation.
I also use it to check how the hills look on certain sections of the route. But for actual route planning and following that route, I use the Bikeline map books (though I tend to tour in Germany - anywhere else, I look for an equivalent.