The city centre from the nearby Port Hills immediately after the earthquake (Click to enlarge, photographer/source unknown):
Series of shots from The Atlantic.com (warning, a couple of these might be distressing):
Before and after shots from the NZ Herald:
The backpackers in shot 2 is the one Fi and I stayed at in 2003 (for those who know the story it is the one where the early morning amorous couple in the common lounge incident occurred). From memory our room was in the completely wrecked portion and it is chilling to see it this way.
A similar interactive before and after from news.com.au:
Video of a rescue from one of the collapsed buildings: