Okay, correct if I'm wrong then, since you've seen it way more times than me, you lucky lady ;) but:
Coulson says, "Tasha, Barton's been compromised."
She introduces herself to Bruce as Natasha Romanoff.
Coulson says Agent Romanoff when she first shows up on the hellicarrier.
Clint calls her Tasha when he gets bonked over the head, then it's Tasha and one Natasha when they're in the infirmary, and then Nat the two times he addresses her over the comms during the big fight.

Am I missing any?

(Because seriously, I am having thoughts about names like woah.)