If no heirs can be found, this could even be long lost cousins etc, then, in the UK at least, all property/belogings/money go to the government which they then auction off. Then that money gets put in the governments coffers. I don't think anything specfically, though using it as aid money would seem best.
There is a TV show in the UK that shows how companies look at a publicly available list of people that have pasted without any immediate next of kin. They then look through censuses etc for family history and find the heirs, for those with estates left that have so much worth, so they can recoup their costs and make a profit. The heirs then sign a contract with the company so that the company will deal with all the legal stuff and paper work in return for 10-15% of the inheritance.
http://en.wikipedia.org/wiki/Heir_Hunters