To generate random alphanumeric strings drop the following into your zshrc:

  function mkpw () {
      if (( $# == 0 )) then
          head /dev/urandom | uuencode -m - | sed -n 2p | cut -c1-${1:-12}
      else
          head /dev/urandom | uuencode -m - | sed -n 2p | cut -c1-${1:-$1}
      fi
  }

By default it generates an alphanumeric string of length 12. Given an integer argument n it generates an alphanumeric string of length n.