For the foreshadowing pile:

Chapter 20 (on the Pioneer plaque):

"So I am going to violate rule two - which was simply 'don't brag' - and tell you about something I have done. I don't see how the knowledge could do any harm. And I strongly suspect you would have figured it out anyway, once we knew each other well enough."

Chapter 46:

"Tell me, Mr. Potter, if you wanted to lose something where no one would ever find it again, where would you put it?"

Harry considered this question. "I suppose I shouldn't ask what you've found that needs losing -"

"Quite," said Professor Quirrell, as Harry had expected; and then, "Perhaps you will be told when you are older," which Harry hadn't.

Edit: Chapter 49:

"One might even regret your infant self's victory," said Professor Quirrell. His smile twisted. "If only You-Know-Who had lived, you might have persuaded him to teach you some of the knowledge that would have been your heritage, from one Heir of Slytherin to another." The smile twisted further, as though to mock the obvious impossibility, even given the premise.