ksh

        while :; do print "Hello World!"; done

submitted by: chongo@prime.corp.sgi.com Landon Curt Noll

And another interesting version.....

#!/bin/ksh
set -A MSG "\041" "\0144" "\0154" "\0162" "\0157" "\0127" "\040" "\054" "\0157" "\0154" "\0154" "\0145" "\0110"

while true;do
  integer INDEX=12
  while [[ $INDEX -ge 0 ]];do
    print -n ${MSG[${INDEX}]}
    INDEX=$((${INDEX}-1))
  done
  print
done

submitted by: scottie@sequent.com (Scott Thurston)