some have been mentioned already.

The most important you sort of mentioned already. It's hard to see how Rand and Egwene will come to an agreement on their own. Moiraine is someone they both respect and trust. I think she will help with that. Toward the end, Moiraine and Egwene were getting along almost as friends. Nynaeve and Elayne are the other two who they are both friends with, but I don't think Egwene trusts them as much as she trusts Moiraine.

The second most important is with Callandor. Rand tells Nynaeve in Towers of Midnight he wants someone he can trust to use it. His thought at that time is "Perhaps Elayne or Aviendha." The moment I read that, I immediately thought of Moiraine. He's not going to pick Elayne over Aviendha or vice versa. It's just fitting that Nynaeve and Moiraine be there with him at the end. The best argument I've seen against this is that Moiraine is a weakling now, but I've never considered that relevant, and neither does Rand . He wants someone he can trust, not someone who's uber powerful. Plus, she can use her angreal at the same time.