These are some data sources that, at some point in time, made my day. They might be very well-known, but I did not know about them when I was looking for them. I arrange them below by topic.
Poverty, inequality and welfare in the US
National Welfare Data - University of Kentucky Center for Poverty Research
Includes U.S. state level economic and program transfer data covering the years 1980 - 2019, assembled from different sources
State-level income inequality
Data on state-level income inequality from 1917 to 2015, where inequality is measured by the share of income of top percentiles. The dataset is created by Sommieller and Price using data from the Internal Revenue Service SOI Tax Stats.
China's Aid and Investments
China's Global Investment Tracker - American Enterprise Institute (AEI)
Covers China’s global investment and construction in all countries from 2005 onwards. Includes information about the amount of each project, Chinese parent company, host country, and sector.