CommodityFACT.org is a gathering of useful data and research that are all commodity related. The site provides a good, no-nonsense introduction to commodity derivatives and their applications, as well as a great overview of recent studies of commodity markets.
Quandl is a large online database of time-series datasets. Here you can find spot and futures prices of a large number of commodities and indices. The site also provides other types of financial and economic data, like e.g. currency series, rates and so on. All of Quandl's datasets are open and free.
IndexMundi is a data portal that gathers facts and statistics from multiple sources, and presents them in the form of easy to access tables and visuals. IndexMundi provides a large range of economic time-series, including a section on commodities. Here you will find historical prices, import and export statistics, production data and more.
FAOSTAT is run by the statistics division of the FAO, and offers free and easy access to data for 245 countries and 35 regional areas from 1961 through the most recent year available. Here you can find large time-series and cross-sectional datasets related to food and agricultural products.
Commodity HQ offers educational content, analysis, and commentary on global commodity markets. In the article 15 Commodity-Friendly Professors they mention some of the pioneers in the field of commodity investments. This is a great place to start looking for research papers that focus on commodity markets.