For one quick referrence on externalities see E.K. Hunt and R.C. D'Arge, "On Lemmings and other Acquisitive Animals: Propositions on Consumption," Journal of Economic Issues, June 1973. For one quick illustration: One recent study of 500 consumer goods concluded that market prices diverged from social opportunity costs on average by 20% due ONLY to the market's failure to incorporate the external costs of disposal of packaging the items came in.
