Matt Graham wrote: 
xset dpms force off  # to turn off

This worked from a shell, I don't know if it will work in cron
    

At the very least, you need to set DISPLAY to :0 , as cron jobs have
a really limited set of environment variables.  The cron job also
must be running as the user who's currently using the X Display.
Or you could just do "xhost +local:", though that will cause paranoid
people to have a cow.

Yep I figured that out as well.  Here is what I am using for tonight, I will come up with a more graceful script tommorrow :-)

[bigscreen@bigscreen ~]$ cat /usr/local/bin/display.sh
#!/bin/bash
export DISPLAY=:0.0
PARAM=$1

if [ "off" == "$PARAM" ]; then
   echo "Turning OFF screen via dpms..."
   export DISPLAY=":0.0"
   /usr/bin/xset dpms force off
   exit 0
elif [ "on" == "$PARAM" ]; then
   echo "Turning ON screen via dpms..."
   export DISPLAY=":0.0"
   /usr/bin/xset dpms force on
   exit 0
fi

echo "Usage: $0 on/off"
echo "        This will turn the display on or off via dpms." 

I tested this from cron as the user running the X session and it appears to work :)