You don't say how you want to stop these pings, but essentially there are two parts to a ping: an ICMP Echo Request and ICMP Echo Response.

These two are ICMP Type 8 and ICMP Type 0 respectively.

To block incoming echo requests (when someone pings your machine ignore it):

iptables -I INPUT -p icmp --icmp-type 8 -j DROP

If you are acting as a router/firewall for a network, you would place this in the FORWARD table:

iptables -I FORWARD -p icmp --icmp-type 8 -j DROP

It is generally a sensible idea to drop any unsolicited responses, so I would have the following in my INPUT table:

iptables -A INPUT -p icmp --icmp-type 0 -m state ! --state RELATED,ESTABLISHED -j DROP

Very simple solution

echo 1 >/proc/sys/net/ipv4/icmp_echo_ignore_all

A ping is a simple echo request using the Internet Control Message Protocol (ICMP), so the following should work:

iptables -A INPUT -p icmp --icmp-type 8 -j DROP.

ICMP type 8 is echo as specified here: http://www.iana.org/assignments/icmp-parameters