At which point in the Harry Potter books was it clear with no ambiguity that Ron himself (as opposed to Harry, Hermione, or Rowling) is aware that he is romantically attracted to Hermione? I would prefer an actual quote from the book, or JKR.
“I love you, Hermione,” said Ron, sinking back in his chair, rubbing his eyes wearily.
Hermione turned faintly pink, but merely said, “Don’t let Lavender hear you saying that.” (Half-Blood Prince, Page 440.)
I think that's the moment.
It must have been one of the happiest days of her life, for Hermione. :)
I think it's after Ron was poisoned in the 6th book, Harry Potter and the Half Blood Prince. When Lavender Brown comes to visit him in the hospital, he pretends to be asleep. He seems to only want Hermione's presence, not Lavender's. I think that is the time that he realizes that he is in love with Hermione.
From Goblet of Fire, when they're talking about needing partners for the Yule Ball:
But Ron was staring at Hermione as though suddenly seeing her in a whole new light. "Hermione, Neville's right - you are a girl..."
Of course, Ron then says she can go with "one of us" (him or Harry, not just him), and says he's asking because they need partners. Still, the "whole new light" part implies that he may be finding her attractive for the first time.