Personally, I had never used the United States (US) National Archives databases until a few years ago, when I started using the Numident Files, which are a fantastic resource. I get lost in it!
NARA has a great list of Genealogy Research Topics, which are links to further detailed discussions about the topic, as well as guides to other relevant resources and links to collections (both online and offline). Here is a list of current topics and links:
African-American Research
www.Archives.gov/research/african-americans
Aliens
www.Archives.gov/research/immigration/aliens/
Bankruptcy Case Files
www.Archives.gov/kansas-city/bankruptcy-case-files
Caring for your Family Archives
www.Archives.gov/preservation/family-archives/
Census Records (1790-1940)
www.Archives.gov/research/census/
Chinese Immigration
www.Archives.gov/research/chinese-americans
Citing records in the National Archives of the United States
www.Archives.gov/publications/general-info-leaflets/17-citing-records.html
Congressional Records: Private Claims and Private Legislation
www.Archives.gov/publications/prologue/1995/spring/private-claims-1.html
Court Records
www.Archives.gov/research/court-records/
Electronic Records for Genealogy or Other Personal Research
www.Archives.gov/research/genealogy/electronic-records.html
Ethnic Heritage Research and Resources
www.Archives.gov/research/genealogy/ethnic-heritage.html
Exploration and American Expansion
www.Archives.gov/research/land/exploration-expansion
Federal Employees
www.Archives.gov/research/federal-employees/
Immigration Records
www.Archives.gov/research/immigration/
Income Tax Records of the Civil War Years
www.Archives.gov/research/genealogy/tax-records
Internal Migration
www.Archives.gov/research/exploration-expansion
Japanese Americans
www.Archives.gov/research/japanese-americans/
Land Records
www.Archives.gov/research/land/homesteads
Maps of interest to Genealogists
www.Archives.gov/research/genealogy/maps
Maritime
www.Archives.gov/research/maritime/
Microfilmed Records
www.Archives.gov/research/start/by-format.html
Military Records
www.Archives.gov/research/military
Native American Records
www.Archives.gov/research/native-americans/
Naturalization Records
www.Archives.gov/research/immigration/naturalization
Naval Records
www.Archives.gov/research/military/navy/
Passenger Lists
www.Archives.gov/research/immigration/
Passport Applications
www.Archives.gov/research/genealogy/passports/
Post Office Records
www.Archives.gov/research/post-offices/
Pre-Federal Records
www.Archives.gov/research/pre-federal/
Prisons
www.Archives.gov/research/prisons/
Social Security Records
aad.Archives.gov/aad/series-list.jsp?cat=SB2046&bc=sb
State Department Records of Genealogical Interest
www.Archives.gov/research/foreign-policy/state-dept/genealogy.html
Tax Records
www.Archives.gov/research/genealogy/tax-records
Vital Records
www.Archives.gov/research/vital-records
Women
www.Archives.gov/women/notable-women
I also recommend that you read the National Archives Catalog Guide for Genealogists and Family Historians.
www.Archives.gov/research/genealogy/catalog-guide
You will find many databases above in the list of Resource Topics. There is an important page that you should then peruse. It is Access to Archival Databases
There are several links that help you to find online databases and indexes.
Click HERE for other Free Online Genealogy Websites of the Day
