Here's a quick and easy room fragrance idea I just tried myself: warming cinnamon. I got the idea from http://www.thriftyfun.com/tf766832.tip.html and I modified it slightly:
1) Put about 1/2 inch of water in a small pot.
2) Add cinnamon, nutmeg and vanilla.
3) Simmer for about 2 minutes.
It creates a beautiful, Christmas baking fragrance that permeates the house. I then left the pot on the stove top with the burner off, so that I can use the mixture again later when the fragrance fades.
The net result is a festive, comforting aroma that is fast, easy, and chemical free!