http://nginx.org/en/linux_packages.html#stable

sudo apt-key add nginx_signing.key

deb http://nginx.org/packages/debian/ codename nginx
deb-src http://nginx.org/packages/debian/ codename nginx

deb http://nginx.org/packages/ubuntu/ utopic nginx
deb-src http://nginx.org/packages/ubuntu/ utopic nginx

apt-get update
apt-get install nginx