In no particular order
Dataset sources
In no particular order
More
El catastro
(Spain's real state data) https://www.sedecatastro.gob.es/
Open listings
In the shape of a newsletter
UCI Machine Learning repository
Wikipedia's List of datasets for machine-learning research
https://en.wikipedia.org/wiki/List_of_datasets_for_machine-learning_research
Registry of Research Data Repositories
Zenodo
Url
About
Focused on
Open Science
Hosted by
CERN
Gated listings
Requires signup
Requires passing an application
Accessed through BigQuery
Might require payments (pricing)
Datasets
Flickr1024: A Dataset for Stereo Image Super-resolution (on Arxiv)
A collection of small corpuses of interesting data for the creation of bots and similar stuff.
a 6.4 TB dataset of permissively licensed source code in 358 programming languages.
IMDb datasets
Url
Frozen full data from 2017
Search engines
Google Dataset Search
City/Country data portals
Portal de datos de Barcelona
Portal de datos de Madrid
Portal de datos de España
Portal de datos de la Generalitat de Catalunya
London Datastore
NYC Open Data
NOAA Coastal Science portal
European Union Open Data Portal
U.S. Government’s open data