There are a number but a few stand out as set out below and some more general comments :-
BCAL 707 from South America in mid 70,s which I got to go to the flight deck on as a school boy when level with Dakar. Was then invited back to stay until landing in LGW if I wanted, as nobody else asked for a cockpit visit
Cathay 747 into HKG also on flight deck in mid 1980,s pilot was a freind so got bumped to 1st Class as well
.
As has been commented on before, many views of large Aurora displays - never bores me
. Also big electrical storms at night in the tropic,s as long as not in them !.
Sun rises and or sunsets, latter with G&T always good
.
The cabin crews from many airlines and cultures who have largly helped keep me sane, and looked after me and chatted on those long trans oceanic / trans continental flights where the moving map appears to belie the comment that the world is getting smaller
!.
Flight to Dallas in Mid July 1987 when it was deemed by my then employer that I had reached the point where the world of Business class travel was to be opened to me - spoilt for life as far as air travel is concerned from then on
.