My family ran a mechanical company and we did Geo Installs. It is a great system that can be modified depending on your situation.
I always sold it as pay more now or pay more later. Most reputable dealers should be able to give you payback chart showing your savings to pay for the system. Say good bye to the natural gas bill as most systems can run your heating/cooling and domestic hot water. They can also run in floor (radiant heating). All you pay is the electricity to run the circulating pump and fan if going forced air.
I included some links to suppliers we used:
http://www.icekubesystems.com/htmlfi...heat-pumps.asp
http://www.waterfurnace.ca/
Also a good source of info for us Canucks:
http://www.geothermal.ca/