Alex Popenkov

server {
    server_name  www.mydomain.com;
    listen 80;
    return 301 http://mydomain.com$request_uri;
}

server {
    server_name  www.mydomain.com;
    listen 80;       
    if ($http_host = www.mydomain.com) {
           rewrite ^(.*)$  http://mydomain.com$1 permanent;
    }
}

server_name site.com www.site.com
listen 1.2.3.4;
if ($host ~* www\.(.*)) {
		  set $host_without_www $1;
		  rewrite ^(.*)$ http://$host_without_www$1 permanent;
}