Security system... ADT or similar... doesn't even have to be monitored, but a fully wireless system is easy to install and are pretty invisible.
Wooden dowels in all the windows.
Stickers on all the windows.
Dog (or at least some "beware of dog signs" and a doghouse in the backyard... bonus points for "Zeus" on it)
CCTV system... can be had very cheap nowadays, but to do a 4-chan NVR system the right way with good cameras, it's going to be $1000-$1500.
"NO SOLICITING" sign at front door.
Front door camera system so you don't have to approach the door or look through the peephole to see who is there. The wireless receiver and 2-way comms in this unit is pretty sweet.
http://www.amazon.com/Entry-Guardia...&keywords=front+door+security+camera+wireless
Do a thorough inspection of the outside of your home. Don't leave any tools or equipment laying around outside that somebody could use to break a window. Limit access to windows with bushes.
Enroll your neighbors in your security plan... overlapping defenses and what not. Keep up to speed on crime in your area by making friends with local cops who will keep you informed on the local blotter. Consider starting a Neighborhood Watch or volunteering if there's already one. Learn local response times and maybe take a ride-along or two for brownie points.
Learn all the vehicles in your neighborhood and take a drive through all your local streets once a week or until you're intimately familiar with what looks "normal"... that way when something is amiss, you'll spot it.
Criminals often canvass entire neighborhoods at a time, then strike many houses in the same location in a very short period of time if not the same day.
Ensure you are intimate with the self-defense laws in your state regarding use-of-force inside/outside the house and so on.
Most importantly... have a plan. Go over a few different scenarios with the family so they know exactly what to do in a crisis. You should discuss scenarios when they are home alone or you are together. You should discuss scenarios where there are non-family members present who don't know what to do, and the correct way to get them to perform under stress.