As several people mentioned before:
Approaching SFO via Point Reyes, Golden Gate Bridge, SF Bay and Redwood Shores on crisp and clear day.
Especially awesome when sitting in the cockpit jump seat on a 747-400 from Europe (happened once. I am still in awe...)
Also flying in Finland over the lakes in a 16 seater plane on a clear summer day. IIRC it was from Savonlinna to Jyveskulaee.