When thinking about preparedness for emergencies where services such as water, gas, electricity, etc. may be shut off or otherwise unavailable, you must think back to about 100+ years ago. How did they control their indoor temps? My suggestion is to install a wood burning stove where your fireplace is located (they make good inserts). They also have free-standing models available. This uses readily available flamable fuel and can be used to cook with.

My grandparents and brother-in-law have a wood burning stove insert and a freestanding one (respectively) and they can heat their whole house (keep doors open to all the rooms).

The other (cheaper) option would be to invest in a kerosene or propane space heater. I'm not familiar with the larger ones but Walmart and their ilk sell a cataiytic propane space heater (uses the small disposable cartridges) for about $30 dollars. It won't heat your house, but it might help take the chill off a smaller room in your basement. Of course with all improvised methods of heat, remember to have a carbonmonoxide detector (battery powered) and fire extinguishers handy. You also would have to worry about storing containers of fuel in your house with this method.

Look here for examples (I neither endorse nor sell these products so use at your own risk)
http://www.coleman.com/coleman/ColemanCom/subcategory.asp?CategoryID=3000

Or something larger like this:
[Link didn't work] go to www.homedepot.com then in the search bar, type in portable propane heater.