Aragorn is 88 years old when the story starts but when he asks Legolas his opinion on the Fangorn forest, Aragorn is told "You have journeyed further than I. I have heard nothing of this in my land, save only songs that tell how the Onodrim, that men call Ents, dwelt there long ago; for Fangorn is old, old even as the Elves would reckon it." (p. 463) Does this sound like it would come from someone who is almost three thousand years old? It's hard to believe he is at least 500, though he does say later on, "It is old, very old. So old that almost I feel young again, as I have not felt since I journeyed with you children. It is old and full of memory. I could have been happy here, if I had come in days of peace." (p. 512)

I have also read on other sites that Legolas in the book called others in the fellowship names. I only found one reference, but will keep looking for others. The mention is Merry, who he calls Master Sluggard (once, for all I could find). This was not done to be mean or childish. Merry slept in, while everyone else was up and about. The definition of sluggard is: a person habitually lazy, idle, and inactive. Though it can be considered an insult, I think Legolas was just referring to Merry being so tired (idle? inactive?), "The sun is high. All others are up and going. Come, Master Sluggard, and look at this place while you may." (pp 806-807)

There is also little mention to what Legolas looks like. I won't spend much time on this, since several sites already delve into it. It is said that his father is blonde (from The Hobbit), so it's a fair guess that Legolas is as well. Following are the quotes I found:
"There was a strange elf clad in green and brown, Legolas, a messenger from his father, Thranduil, the king of the elves of Northern Mirkwood. (p 257) Legolas stood before the gate and turned his bright eyes away north and east, and his fair face was troubled. (p 807) ...for Legolas was fair of face beyond the measure of men, and he sang an elven-song in a clear voice as he walked in the morning...(p 906)

Several times his eyesight is mentioned..."But Legolas stood beside him, shading his bright elven-eyes with his long slender hand, and he saw not a shadow, nor a blur, but the small figure of horsemen...beyond the edge of mortal sight." (p 450) From Gandalf to Legolas:
"You have the keen eyes of your fair kindred, Legolas, and they can tell a sparrow from a finch a league off."
"Many miles lie between," said Legolas, gazing thither and shading his eyes with his long hand. "I can see a darkness...It is not mist or cloud that defeats my eyes: there is a veiling shadow that some power lays upon the land..." (p 550)

Following is one of my favorite quotes:
"He stands not alone," said Legolas, bending his bow and fitting an arrow with hands that moved quicker than sight. "You would die before your stroke fell."

Where does he get all those arrows? "And I" said Legolas, "will take all the arrows that I can find, for my quiver is empty." (p 433) Apparently, he's not picky about which ones he uses, only that they are long enough and in good shape.

Whose horse is that? Well, apparently Arod is not Legolas' horse. Eomer loaned him the horse when they met (p. 461). Legolas even had them remove the saddle, so poor Gimli was forced to ride behind him without it aiding him. At least they didn't do that in the movie.

Does he sleep? "Legolas already lay motionless, his fair hands folded upon his breast, his eyes unclosed, blending living night and deep dream, as is the way of elves...Gimli was still deep in slumber, but Legolas was standing, gazing northwards into the darkness, thoughtful and silent as a young tree in a windless night (p. 445)...As before Legolas was first afoot, if indeed he had ever slept" (p 447). Apparently, he can even sleep while he is walking around, "Only Legolas still stepped as lightly as ever, his feet hardly seeming to press the grass, leaving no footprints as he passed; but in the waybread of the Elves he found all the sustenance that he needed, and he could sleep, if sleep it could be called by Men, resting his mind in the strange paths of elvish dreams, even as he walked open-eyed in the light of this world." (p 448)

I heard of a pact made between Legolas and Gimli, since they travel together and even end up sailing to the Undying lands together. What is this pact, I wondered:
Gimli wants them to visit the glittering caves and Legolas responds. "Nay! There is no time. Do not spoil the wonder with haste! I have given you my word to return hither with you, if a day of peace and freedom comes again..." (p 807) After Aragorn weds Arwen, Legolas repays his promise to Gimli, and they go visit the Glittering caves and then return to the forest of Fangorn. (p 1014)

While Legolas is in Gondor, he sees gulls and says, "...then I stood still, forgetting war in Middle-Earth; for their wailing voices spoke to me of the sea! The sea! Alas! I have not yet beheld it, but deep in the hearts of all my kindred lies the sea-loving, which it is perilous to stir. Alas! for the gulls. No peace shall I have again under beech or under elm. (p 907)...Alas for the wailing of the gulls! Did not the lady tell me to beware of them? And now I cannot forget them! (p 909) He then sings about the sea. Following is that song:

To the sea, to the sea! The white gulls are crying;
The wind is blowing, and the white foam is flying.
West, west away, the round sun is falling.
Grey ship, grey ship, do you hear them calling,
the voices of my people that have gone before me?
I will leave, I will leave the woods that bore me;
For our days are ending and our years failing.
I will pass the wide waters lonely sailing.
Long are the waves on the last shore falling.
Sweet are the voices in the Lost Isle calling.
In Eressea, in Elven home that no man can discover.
Where the leaves fall not: land of my people for ever!