This article on MSN Money details the various ways in which we literally waste money. Personally, I waste money through library fines, food spoilage, buying more clothes than necessary (my wife actually), not sending in mail-in-rebates etc.
Ever notice how city council increases late-fees on library items every year? It is a nice increasing revenue stream for the local government and they can rightly blame us and get away with it!
The article mentions that we waste about 10% of our grocery dollars through spoilage. Sadly, I think it is true with us and we have to do a better job on managing the fridge inventory.