There are so many -
1. Jack and Ennis in the dozy embrace - Jack with his eyes closed, his bittersweet expression of total fulfillment mixed with the pain of knowing Ennis is leaving, and Ennis' loving expression when he sings to him. God, I'm tearin' up just thinkin' about it!
2. Ennis and Jack, the second night in the tent - Ennis goes to Jack with a look of total vulnerabilty and surrender on his face. He never looked as vulnerable throughout the entire movie as he did then. And of course, Jack with his reassuring expression and unwavering look into Ennis' eyes, telling him he's there for him and that everything's all right. I have to think sometimes that Jack was the stronger one, at least when it comes to their relationship.
3. Jack, when they came down from the mountain early, there are actually a couple here - when they talk about possibly coming back next summer. He looks down, then looks up hopefully when he says "I might be back, if the Army don't git me." When Ennis is non-committal, his look of shock and disappointment just floored me - it's as if he's saying, "how can you walk away after all that happened between us? without words, only his facial expressions.
4. Jack again, driving to see Ennis after the divorce, face full of hope and flying high on love, looking like he was just about going to kiss Ennis, only to have his hopes dashed when Ennis turns him away. He looks a bit confused, then a look of realization and disappointment sets in, when Ennis is uncomfortable that someone might see them, and Jack turns to see the white truck drive by. He cries in the truck and then pulls himself together, pushing his feelings down inside. He then goes to Mexico and meets with the prostitute, and he has the most lost look on his face.
5. Ennis, when Alma tells him she's tired of living at the ranch and wants to get a place in town, and she says something to the effect of "you don't want to be so lonely like how it was when you grew up" and it's like she shot him through the heart, his eyelids flutter a bit and he has an expression of heartache.
6. Jack, dancing with Lureen at the rodeo bar, looking like he's really thinking of and missing Ennis when the band is playing "Noone's Gonna Love You Like Me".
6. Alma, when she's become used to Ennis' trips away and she's sitting at the table showing very little emotion, maybe suppressed anger, as Ennis is hurring to leave, she's become resigned to the way things are between them. She says to Ennis "you forgettin' sumthin'?" Ennis hesitates and almost seems be considering whether to kiss her goodbye or not, but Alma is referring to his fishing gear, doesn't even expect anything else.
Sorry to have written a short story about the facial expressions! There are many, many more - I think Jake said that this was a story that was told with very few words or something like that!