Big roundabout between Alexandria and Balloch OK? (Got some weird piece of 'art' on it, can't miss it.) Everything north of that and everything west of that. Everything.
A little more helpfully, try
Good Biking Roads In Scotland and
Post Your Best Roads both threads of this parish.
For me it's the A890 between Kyle of Lochalsh and Achnasheen. Bloody hell.
Enjoy!