I think Iron Man's best action scenes weren't in the trilogy, but rather The Avengers.
1. Germany Entrance vs. Loki - that was total win, swooping down, repulsor to the face, and the Iron Man landing.
2. Iron Man vs Thor - battle of the Titans, with the whipped cream on top being Thor's finisher on Cap's Shield.
3. First run against the Chitauri - that full speed upward flight with the twists, the mini-Repulsor bombs and keeping on even after getting clipped by one of them,
4. All In Fight Sequence - firing, while flying backwards, then dropping down, blowing away a few baddies, and clearing the rest by Repulsor blast off of Cap's shield!
5. Nuke run - this for me was one of the most tense moments of the movie, and honest to God, the first time I saw it, I wondered if Iron Man was truly on a one-way trip.
Off those, my personal, hands-down favorite is #4, with the Repulsor-Cap's Shield combo.
All of these scenes, in my opinion, top all of the action in Iron Man 1-3. However, I would give notable mention to the following:
1. Gulmira - By far my favorite of the trilogy fights, topped off by being chased by jets at Mach speeds.
2. Drop your socks - The flight through the water fountains at the Stark Expo while being chased by War Machine and the Hammeroids was pretty darn good, and well shot in my opinion.
But, again, neither of these felt as epic as the IM action in The Avengers.