USDA Nutrient DB (R Data Package) by Hadley Wickham.
From the webpage:
This package contains all data from the USDA National Nutrient Database, “Composition of Foods Raw, Processed, Prepared”, release 26.
From the data documentation:
The USDA National Nutrient Database for Standard Reference (SR) is the major source of food composition data in the United States. It provides the foundation for most food composition databases in the public and private sectors. As information is updated, new versions of the database are released. This version, Release 26 (SR26), contains data on 8,463 food items and up to 150 food components. It replaces SR25 issued in September 2012.
Updated data have been published electronically on the USDA Nutrient Data Laboratory (NDL) web site since 1992. SR26 includes composition data for all the food groups and nutrients published in the 21 volumes of “Agriculture Handbook 8” (U.S. Department of Agriculture 1976-92), and its four supplements (U.S. Department of Agriculture 1990-93), which superseded the 1963 edition (Watt and Merrill, 1963). SR26 supersedes all previous releases, including the printed versions, in the event of any differences.
The ingredient calculators at most recipe sites are wimpy by comparison. If you really are interested in what you are ingesting on a day to day basis, take a walk through this data set.
Some other links of interest:
Correlating this data with online shopping options could be quite useful.