Most powerful scene in TNG without dialogue.

[Mutai Sho-Rin]

Another brief but powerful moment is in Lower Decks. Worf is looking out the shuttlebay after Sito Jaxa has left for Cardasia. His body position says it all.

http://tng.trekcore.com/gallery/albums/s7/7x15/lowerdecks325.jpg

 

[Alpha Flyer]

The Inner Light and Wolf 359, definitely. And assuming singing doesn't count as dialogue, O'Brien and Maxwell sitting and singing "The Minstrel Boy" in "The Wounded", just before Maxwell gives up. A study in regret, defiance and compassion.

 

[Flying Spaghetti Monster]

I wanted to add one to the list, after watching the episode last night during dinner.

The scene in "Legacy", when Riker beams back to the Enterprise, cradling Ishara Yar's unconscious body in his arms. The look in Riker's face and eyes just say it all, as he looks to his shipmates in the transporter room. Very powerful, IMO.

Yes. That is a powerful moment.

 

[Tiberius]

Another brief but powerful moment is in Lower Decks. Worf is looking out the shuttlebay after Sito Jaxa has left for Cardasia. His body position says it all.

http://tng.trekcore.com/gallery/albums/s7/7x15/lowerdecks325.jpg

Actually, that always seemed a little cliched to me...