I only remember three off the top of my head:

1)  During the storm when Bilbo saw the giants tossing
    rocks from the cave in the High Pass.
2)  After the escape from the Goblins, Gandalf said
    something about getting a decent giant to seal
    up the cave's entrance where they were taken by
    the Goblins.
3)  When telling Bilbo and the Dwarves about Beorn
    (prior to actually meeting him), Gandalf speculated
    Beorn's people came from the mountains before the
    giants came, or something like that.  Don't have
    time to check right now.
Michael



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Parma Endorion: Essays On Middle-earth