Data.gov [data.gov] is a wealth, nay, a veritable plethora and multitude of, well, data.
It's hard to describe, almost overwhelming. A bunch of data from all levels of the government that is freely accessible. A big, big, big bunch of data. Recent new additions featured on the home page include:
--Gravesite locations of veterans in Kentucky & Louisianna
--Fruit & Veg market news
--And the always important USDA Database for the Isoflavone Content of Selected Foods
It's a great source of info and app developers are encouraged to come up with new ways of massaging the data.