For Simulations;
http://zombies.sothisisacomic.com/ - This here is an excellent infection simulator, The site is led by Mario Lopez.

For Survival Planning;
http://zombiesurvivalgroup.wetpaint.com/?t=anon - An up and coming site, much like ours, except with a much bigger influence of survival planning.
http://zombiesurvivalists.wetpaint.com/- it a new site but its good



The Zombie Squad:
http://zombiehunters.org/index.php - A very helpful site, with lots of info and a good forum. The group has been around for quite awhile.

FVZA
A more in-depth look at zombie physiology, dynamics and what weapons to use. http://fvza.org/