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.
03/10 - The Sword
03/14 - Rotting Out
03/26 - STYG/Terror
04/01 - Earth
04/03 - MOTM Fest