Yay! I can now ping from the command line on my jailbroken iPod after installing Inetutils from Cydia. Inetutils is a free iPhone app for ping, ftp, inetd, rlogin, telnet and tftp.
Unlike most *nix versions of ping, the inetutils version only sends 4 pings by default. This can of course be easily modified with the -c switch to specify a number of pings.
ping -c 100 google.com