As you might expect, and as reported by Google Maps Mania, there are already a variety of resources available to assist those in the area.
The easiest is the Google Person Finder for Christchurch, to help track down anyone that has been affected by the earthquake. You can use the site if you're looking for someone, or if you know the condition of someone that others may be looking for. As of now, the site already has nearly 5000 records.
I'm very happy to report that Frank Taylor is doing well. He and his wife Karen were in downtown Christchurch when the quake struck, and while they saw a lot of damage around them, they were luckily unharmed. You can read about it on the Tahina Expedition blog, which includes some photos he has just taken in Christchurch.
Another great resource for the quake is this very useful Ushahidi-powered site, which provides information about hospitals, road conditions, hazard zones and other related information. It's an excellent resource to have available if you're on the ground in the area.
Finally, I encourage you to check out the Christchurch Quake Map, which shows all of the quakes and aftershocks in the area for the past year (nearly 5,000 of them). You can filter the map to show only the 55 quakes that have struck in the past 24 hours.
If you're aware of any other great resources, please leave a comment and we'll update this post as needed.