From Get Religion, a link to a story on those candles you see everywhere now – the glass pillars with pictures of saints, etc. printed on the front. An interesting history is related in the story:

Scholars and candle industry folks find their origin hard to pinpoint. According to Sister Schodts Reed, chief executive officer of the Reed Candle Factory in San Antonio, her Mexican-born father-in-law, Peter Doan Reed, invented the prayer candle in the late 1940s.

The elder Reed started making votive candles — which are always burned in glass and are so named for their use when making a vow or petition — in 1938. But after about a decade of making standard votives, Reed, in 1947, came up with a tall jar model that could burn for seven days and bore a picture of a spiritual figure along with a prayer.

"His goal was to allow people to have their particular patron saint with the image on the candle so that they could light it and have their prayer on it," Reed said. "That way they have a silent prayer that is continuing even after they are done praying."

Reed said her father-in-law’s company started out selling just a few types of silk-screened prayer candles and now they produce 350 saint varieties alone, many with paper labels. And this doesn’t count the mystical varieties made by their subsidiary, Mission Candles.