For purposes of this page, data repositories are sites where researchers can store, retrieve, and, most importantly, share their raw research data. They are not to be confused with data collections, in which editors assemble and organize data from a variety of sources (e.g. Reaxys, CRC Handbook of Chemistry and Physics, etc.)
For more information on data management for researchers, see the Research Data Management guide.
To locate datasets other than the ones listed below, try the Google Dataset Search.
DOE Data Explorer - Provides a place to discover scientific research data generated from projects funded wholly or in part by the US Department of Energy. Topics vary from astrophysics to general science to x-rays. Records in the DDE link to open datasets, data collections, or repositories.
Dryad Digital Repository - A curated resource that makes the data underlying scientific publications discoverable, freely reusable, and citable.
Nature Scientific Data - Scientific Data is an open-access, peer-reviewed publication for descriptions of scientifically valuable datasets.