Data Citation Index - Iindexes data sets from selected repositories around the world, and also enables the user to find data sets which cite a particular work.
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.
StatSci.Org Data Sets - Annotated listing of data sets for statistics.
Zenodo - All research outputs from across all fields of science are welcome. Zenodo accepts any file format as well as both positive and negative results. Includes publications, datasets, images, software, etc. Sponsored by CERN.