"aTrueShadows" — "(almost) True Shadows" — is a free library providing drop-shadow effects for arbitrary HTML elements.
"aTrueShadows" is built on powerful XBL technology from Mozilla. Which, by this time, means that it works only in Gecko-browsers.
In a spirit of sharing the ideas courious developers are encouraged to look into the library's code — it's realy tiny, just 2 files. Enjoy!