Hmmmm. Just off the top of my head:
Omaha Beach from Medal of Honor: Allied Assault. Will always be awesome.
The Heat-inspired bank heist mission from GTAIV. Makes me super excited for the heists in V.
As far as bosses go, pretty much all of Dark Souls.
09/02 - Solstice
09/05 - DRI
09/09 - Origin
09/14 - Citizen
09/17 - Mineral
09/18 - Clutch