Not sure what compelled me to do this but here we are. Solely based on what I've done. What is yours?

Sunset at Mix
Mesa Grill at Caesars
Mandalay Bay sports (Caesars close second)
Bellagio fountain show
Bellagio $10 blackjack
Saturday/Sunday brunch at Veranda Four Seasons
NFL Sunday at LVH
Mandarin Oriental bar
Mandarin Oriental spa
Luxor interior/exterior

Honorable mentions:


GoGo dancer blackjack pits at Caesars/NYNY/Monte Carlo
Red Rock Canyon
Pools at Mandalay/Mirage/Caesars/Bellagio
Any Cirque de Soleil show
Craft Steak MGM
Border Grill Mandalay Bay
Wrap around terrace suite at Cosmopolitan
Any gourmet restaurant at Aria
Mon Ami Gabi terrace for dinner
Paris breakfast buffet