EPA Environmental Data Set Gateway
The Environmental Dataset Gateway (EDG) provides a single point to discover and access EPA's Open Data resources.
Ecological Data Wiki
This site is intended to serve as a source for identifying datasets that are useful to the study of ecology and quickly figuring out the best ways to use them. The idea is to use the knowlege and effort of the entire ecological community to compile this information rather than relying on each scientist to contribute information for their own studies. Just think of it as the Wikipedia of ecology data.
The USA National Phenology Network
The USA National Phenology Network consists of a National Coordinating Office (NCO), thousands of volunteer observers and many partners, including research scientists, resource managers, educators, and policy-makers.
USDA Ag Data Commons
The Ag Data Commons provides access to a wide variety of open data relevant to agricultural research and related domains such as agronomy, genomics, hydrology, soils, agro-ecosystems, sustainability science, and economic statistics. Data included in the Ag Data Commons is funded in whole or in part by USDA.
USDA Soil Survey
Web Soil Survey (WSS) provides soil data and information produced by the National Cooperative Soil Survey. It is operated by the USDA Natural Resources Conservation Service (NRCS) and provides access to the largest natural resource information system in the world.
VertNet takes four classic vertebrate networks (FishNet, MaNIS, HerpNET, ORNIS), to combine them into a single integrated data portal.