I use these at my house.

http://www.countryglowsoycandles.com/ncandlewarmers.htm

I have one of the large ones and one of the small ones.

I just use any jar candle and when it's finally warm enough I remove the wick since it doesn't get lit at all. If the jar is a bit small for the warmer holder I just push the jar to one side in it and it finally warms up, but it does take a bit longer like all day to get a liquid wax. But even when it's not liquid it does make a nice scent all day.