Ah...cresting the hill and getting paid by the view! On the nature front, there is riding into a brushy area and hearing the cacophony of birds within the brush. If you were in a car, you'd never even know they were there, but on the bike I can hear them.

On the cycling front, on a large group ride the snick of all those clipless pedals trying to simulatneously engage at the start of the ride.