Postcards from Oz - AU Edition

Well chosen, all. In the case of Londo and Gaius, you can even pin point the big shippy moment of open declaration. Londo, on the day of his death in the "In the Beginning" framing narration: "I had four wives, and in my way, I cared for them. But I loved Centauri Prime. And look what I've done to her!"
And in Baltar's case, it's of course this Gaius-Laura dialogue:

Gaius Baltar: Laura. There's been something I've been meaning to say to you. I wanted to thank you.
Laura Roslin: For what?
Baltar: Essentially, for not murdering me. That can't have been an easy decision to make. But I love living. I love living, and I wanted to thank you for saving my life.
Roslin: I wouldn't be so grateful if I were you. You should know that I told the Admiral that if D'Anna doesn't back down, he should blow the ship to pieces.
Baltar: You what?

Gaius Baltar: this is your life.

In Obi-Wan's case, I suppose you could pick the scene in ANH where he explains to Luke what the Force is?