My favorite bit of poetry that they borrowed from Tolkien and put into the movie is what Theoden speaks when he is being dressed by Gamling in the TT.
"Where now is the horse and the rider? Where is the horn that was blowing?
They have passed like rain on the mountain, like a wind in the meadow;
The days have gone down in the West behind the hills into shadow.
How has it come to this?"
I know it's not a song (actually, in the book, Aragorn sang this unabridged), but it is aboslutely
amazing.
I also like Eowyns chant at Theodred's funeral.