A charge controller is a great addition to any solar array, specifically those that are working above 10 watts on a regular basis. These small devices act as "ON" and "OFF" switches to protect your batteries. They prevent overcharging from damaging your batteries and can provide more advanced charging options depending on the make and model.
Harbor Freight Solar Battery Charger. The freakin thing WORKS!!
If you are buying a solar energy system, make sure your panels can be easily adjusted. As seasons change, so does the angle of the sun. Your panels will need to be adjusted every three months or so. Make sure that you know how to do this or talk to your contractor about seasonal maintenance.