I love how some of these room diffusers smell. I decided to try making my own. The essential oils are initially quite expensive. However, they last a long time... so, if you make diffusers for gifts or put them all through your house you would end up saving money.
Mine is a simple blend of orange and grapefruit oils. I just mixed six drops of each in some canola oil and placed in this little jar I had left over from a Target diffuser.
I searched a bit to find the reed diffusers and found them at Pier One Imports for only $2 for a box of 12. Tip: the oils last longer if they are in a dark bottle. I don't think you are really supposed to use Canola Oil as the base, but it is working ok.
Here is a site with some ideas for making your own. They have a Christmas recipe that would be fun to make and give as gifts-you could start shopping now for cute bottles and tiny vases at yard sales and thrift stores, etc. Some more recipes are here.
Update 4/26/09: The Canola Oil didn't work for very long. I'm looking for a good recipe for diffuser base oil if anyone finds one let me know- thanks!