BitcoinSentiment is a non-profit, ad free site tracking the voters sentiment towards Bitcoin through the means of continuous polling. The idea is to provide the technical means required for tapping into the power of crowd-sourcing.
The quality of the data increases as the number of voters increases and you can contribute, by putting voting widgets on your site. To encourage use of widgets, they are designed to be non-intrusive and to not "steal your visitors".
The data generated on the site if free for use and can be downloaded by anyone.
The site offers a variety of charts, with the purchasing power of Bitcoin plotted in terms of other asset classes such as gold and inflation protected US Treasuries.