Want to block sites from internet adress ? :
create a file with all IP adress you want to block, you could get them from domain name with ping command.
and a script like this :
# parameteter to change
#path to iptables
for IP in `cat $BLOCK_FILE`; do
$IPTABLES -A INPUT -i eth0 -s $IP -j DROP
Naturally it is just an example how the thing could be done, it is not a complete iptables script as it does not deal with flushing rules, load modules etc.. It is intended to include in a firewall script