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.
09/18 - Clutch
09/19 - BMTH
09/20 - Fuzz and Fire 2
09/22 - RA/TA/Radkey ?
09/23 - Crowbar