My goodness...I've got too many things to count.
I've seen...
Personal fireworks exploding all over the city of Seattle (literally dozens going off at any given moment), right at sunset on July 3rd, while on a XC with a student in a 152, staying down low to stay out of SEA's Class B airspace.
Sunset over Mount Ranier while flying an Arrow.
Sunset over the snow-capped peaks of western Montana while instructing a friend in his 182.
Heck, pretty much any sunset from the air is amazing.
Both the Atlantic and Pacific oceans. After spending most of my life in the midwest, oceans still impress me!
A string of planes ahead of me, all evenly spaced and cruising at exactly 90 knots, while I was #6 in line to land my Cessna 140 at the EAA Arlington Airshow, just north of Seattle.
The world upside down (while learning loops in a Citabria).
Waterbombers dropping their loads on a wildfire underneath me (yes, I was above the TFR).
Crossing the barren nothingness of western Nebraska (about a 150 mile stretch) at 500 ft. AGL in my 140. There is NOTHING out there except some cattle and a little farmhouse every few miles.
Multi-million dollar estates in the suburbs of Philadelphia. And I mean multi-million dollar...fountains, landscaping, pools, guest houses, the works.
Flying down the Columbia River gorge, just east of Portland, Oregon, with both canyon walls rising in to the overcast layer above me. Actually, I could say this about several mountain passes, and they've all been beautiful.
Some HUGE race track of some sort in Indiana. It was simply labeled "test track" on the sectional. I've attached a picture of it, as I crossed over at about 4500 ft. AGL. Does anyone know what this is?
The faces of both my parents in the plane with me, while taking them out for a $200 burger in an Aztec. The only time I've flown with both of them in the plane at the same time. Is that too cheesy and sentimental?
Downtown Seattle, Philadelphia, Minneapolis, Kansas City, Portland, etc. Flying low over any major metro area is pretty cool.
And many, many more.
Wow...wow...I'm a really lucky guy.