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.
11/24 - COC
11/30 - GUK
12/01 - E
12/02 - B
12/04 - H
12/07 - TQ's