I suppose it depends on what sort of motorcycling you like but my mate and I are very partial to mountain passes and wanted to ride some of the famous passes used in the old Alpine trials, the Monte Carlo Rally and the old ISDT. We mapped out a route covering some 60 of the various passes and in a month managed about forty of them. Weather beat us on the others, They are so high they can be closed with snow in the height of summer. The obvious passes to do are the GrossGlockner in Austria, the Stelvio in Italy and the Dolomites in general. I warn you, once you start you will keep going back time after time as this is fantastic motorcycling country with very friendly people who LIKE motorcyclists.
Best of luck, 33d6