Here's another for you. In Chapter 8, Nick (speaking to Gatsby, then internally) even tells the reader that he is speaking ironically:
“You’re worth the whole damn bunch put together.” I’ve always been glad I said that. It was the only compliment I ever gave him, because I disapproved of him from beginning to end." First he nodded politely, and then his face broke into that radiant and understanding smile, as if we’d been in ecstatic cahoots on that fact all the time.
Furthermore, you might consider the title itself as ironic. Gatsby is hardly great in any way; even his wealth is ill-gotten.
Sure. How about this line?
"Tom's getting very profound," said Daisy with an expression of unthoughtful sadness.
That's in the first chapter, and the idea of someone noticing profound thought while looking unthoughtful, combined with Tom being called profound when he's just made a racist statement, makes this quite ironic.
Or how about Nick telling you in the first chapter that he's inclined to reserve judgement on people - then spends most of his introduction time judging the other characters he's introducing to you.