Fellow Double Negative animator Emanuele Pavarotti has some great comparison reels on vimeo. Amazingly, I haven't seen them posted anywhere else so I'd thought I'd give them a plug here.
They show cycles and playblasts of his animation followed by the fully rendered shots from VFX projects. They give a very interesting insight to how some shots were put together, also the quality of the animation is brilliant.
Night at the Museum 2
The Chronicles of Narnia: Prince Caspian
And the bizzarre 'Pigmy Puff' from Harry Potter and the Half Blood Prince
More of his work can be found on his website here.