Votive candles. I love them, but they leave behind a cleaning job. It's a simple enough thing to pop them into the freezer - the melted wax should pop out like an ice cube.
I've found another solution by accident. I was cleaning out the votive holders I use as quarter candles. The last time they were used the candles had been pretty liberally rubbed with oils, and I had poured a few drops of oil into the glass cup and smeared the oil all around.
The oil had dried, so imagine my surprise when the leftover glass blobs popped right out without the use of the freezer.
I'll be doing this from now on.