Basically any time the destruction engine is given a chance to shine:
The earthquake that levels dozens of buildings and collapses on top of the player character.
The antenna/tower that falls during the attack on the paratroops.
"Comrades" is a great example, especially during the fight through the EURONEXT building. You can pretty much tear the whole level apart.
The beginning of "Going Hunting." If Hawkins wasn't humming the theme to Top Gun it's likely you were.
So get your fangs out, Hawkins. We're hunting big game today.
Admit it, your jaw dropped when you saw that Su-27 pull a Pugachev's Cobra right in front of you.
While the mission itself is Love It or Hate It, it cannot be denied that the opening setpiece is amazing, especially when the Super Hornet shoots down the cat, climbs, and the Battlefield 3 theme kicks in.
The entirety of "Thunder Run." You start off at the gunner seat of your M1 Abrams with the rest of your company rolling alongside to the sound of Crowning Music of Awesome. Chewing up T-72's that are dumb enough to get in your way, blowing up a battery of BM-21 rocket artillery, and rolling into the outskirts of Tehran, blowing the PLR straight to hell. The whole level is one big CMoA.
Dima. Everything this guy does is awesome, from the HALO jump at the start of 'Kaffarov' to surviving a nuke, this guy is badass.
On the multiplayer front, a patch released alongside Back to Karkand allows the huge radio tower on Caspian Border to fall. When one side only has 10 tickets left, the losing team will enact a Desperation Attack and perform an air strike on the tower. Watching the ensuing damage is pure awesome.
Also on the multiplayer front, some of the crazy stunts you can pull. In particular, the RendeZook, which consists of ejecting from a plane when dogfighting, shooting the enemy plane with a bazooka and hopping back into your own plane to continue the flight. It is as much of a Luck-Based Mission as it is a feat of skill, but when you pull it off, you look like a badass.
In the final mission, beating the asshole interrogator's face on the table. The entire game pretty much built up to that one satisfying beating.