What does Kirito say at the end of SAO? At the end of Sword Art Online (episode 25, ~21:40), Kirito says something in the presence of Leafa, Yui, and Asuna.

 

Despite being shown his lips moving, there is no sound and so the only hint is how his lips move. Since my knowledge of Japanese is far from extensive, I don't have the ability to read what his lips are saying.

What is it that Kirito said to the others in this final episode?
From the corresponding scene in the light novel (volume 4, chapter 9; p. 308):


  キリトは透き【すき】通った視線で一瞬【いっしゅん】アインクラッドを見つめ、しばしうつむいた。その唇【くちびる】が動き、かすかな声で誰かの名前を呼んだようだったが、聞き取れなかった。


Translated,


  With his penetrating gaze, Kirito glanced at Aincrad for a moment, and then cast his eyes downward. His lips moved. It seemed as though he had said somebody's name in a faint voice - but [Yui] couldn't hear him.


In light of this, it is clear that Kirito said somebody's name. It seems, however, that the author chose to leave the identity of the person ambiguous. 

I believe that the standard inference among the SAO fanbase is that Kirito said either Sachi's name or Kayaba Akihiko's name. This seems like a reasonable guess to me, though I'm not sure if there's any other evidence supporting it.