I am finding "The Billion Prices Project" to be valuable.
From the homepage, "The Billion Prices Project is an academic initiative that collects prices from hundreds of online retailers around the world on a daily basis to conduct economic research."
Two of the most prominent benefits I see from the data include that data is available daily and it serves as a comparison and is plotted against the CPI (last available data) for references purposes. The current (as of 11-22-10) "Billion Prices" index value for the U.S. is 100.51.
As well, data is available for a number of countries.
This data from "The Billion Prices Project" should be interesting to monitor going forward...
A Special Note concerning our economic situation is found here
SPX at 1180.73 as this post is written