Cusco Motorcycle Rental
The Cusco Motorcycle Rental is one of the best places to hire a motorbike in Peru. It offers cheap prices, great service and a good selection of bikes. The only downside is that they don't have any English speaking staff, but luckily there are plenty of people around willing to translate. If you need to speak Spanish, then they offer free translation services.
You can book your bike here: http://www.cuscomotorcycles.com/en/index.