The Minnesota Population Center is the place for Census microdata. I work primarily with American Community Survey data and Current Population Survey data. When I need zip-code level Census data, I use Census’s American FactFinder.
Behavioral Risk Factor Surveillance System
The CDC’s Behavioral Risk Factor Surveillance System is an annual survey that asks various questions related to health. You can download the annual survey data here.
Population Representation in the Military Services
CNA produces this for the Office of the Under Secretary of Defense for Personnel and Readiness. It’s a good source of information about applicants for military service, people who join the military, and people currently serving in the military. There is also some historical data. The focus is on the Active Component, but there is some information about the Reserve Component as well.
American Time Use Survey
The American Time Use Survey is a Bureau of Labor Statistics program that collects data from 24-hour time use diaries. The most user-friendly way I have found to get their data is through this survey extract builder.