As a library technician and book lover, I have to say that the most intriguing episode I've seen is Silence in the Library. The concept of a whole planet as a library is like my idea of heaven; unlimited access to every book ever written would be amazing. Alas, the concept was flawed, and I am not immortal, anyway.
My top episodes of the revival have been: 'The Empty Child' & 'The Doctor Dances,' 'Silence in the Library' & 'The Forest of the Dead,' 'Blink,' and 'Vincent and the Doctor.' The first two because of the spooky little boy looking for his Mummy, and the end of the second part is good. The library episodes I love largely because of the animated spacesuits, and the Vashta Nerada. Blink is awesome because of the evil ambulatory weeping angel statues, and all the 'timey-wimey' goodness. 'Vincent and the Doctor' is a very moving episode. Very well done, I thought.
It was pretty bad-ass when Rose went Bad Wolf at the the of Parting of Ways.
But as far a favorite episodes, Silence in the Library/The Forest of the Dead was great. So was Blink. I also really like The Impossible Planet/The Satan Pit.
The endings of Doomsday and Journey's End are rather moving though.
My top 5
4) The Eleventh Hour
5) Satan's Pit