List Title
Data
While data visualization is fun and creative, you can't expand your abilities as a data designer without new and challenging data. I try to tackle a new data set every week. That being said, data is everywhere and it can be difficult to identify what is usable and what is not, so this is your one stop shop for usable data on the web.
Google has created a search engine just for datasets. The other web pages included in this list are actually used in the engine, so it can be a nice one-stop-shop.
This is a site dedicated to data science in particular, so it has a pretty good running catalog of datasets submitted by people and other entities. I enjoyed the Simpsons and South Park data.
This is a great Google sheet based on the weekly newsletter, Data is Plural.
For those that use Tableau, these are Web Data Connectors that have been written by the Tableau Community. An easy access playground of data when leveraging Tableau.
A community created to share and collaborate on datasets covering any and all topics. You'll need to sign-up, but it's well worth it.
In 2009 the US government started opening up their data to the public via a single source website. There is a healthy amount of information on this site ranging from census data to hourly precipitation.