A 2007 report by McKinsey ('A cost curve for greenhouse gas reduction') highlights the importance of efficiency in buildings and vehicles, the need to engage power producers and industrial companies with long term incentives, incentives for specific technologies such as carbon capture and storage, and addressing the potential of forestry and agriculture.
The pertinent question, as always, given that energy efficiency can lead to so much gains, why has this not been done before? (Eg. negawatt power). In other words, which existing (maybe often non-monetary) costs are not counted?