Domestic -
LGA (hands down) - even as a native NYers flown the route 100s (if not 1000s) - I still look out the window like a kid.
LAS - great on the right side (arriving from the East) to suddenly see the strip and all the offerings.
International - can't add here as most flights I'm too tired or unable to see.
SDU (isn't bad)
LHR (no fog depending on path to airport) is great