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.
2/19 - 1349
2/26 - Nappy Dappy
3/8 - Title Fight
3/17 - New Found Glory
4/7 - Weedeater