The below list/links includes both fee-based & free genealogy research sites. Another list is online at: 101 Ways to Research Your Family Tree for Free.
BEWARE that much of the information on these sites was compiled by amateur genealogists… and often contain errors. When researching an ancestor, focus on obtaining records / objective evidence to support any claims made. And because many ancestors share the same (or similar) name as others at that time and in that area, who are not related, verify (through the name of their wife / children, etc.) that the person you're collecting information about is the correct person.
Professional Genealogists are also available for hire:
Sons and Daughters of WWII veterans
Order of the Second World War
Order of the First World War
Sons of Confederate Veterans
Military Order of the Stars and Bars
United Daughters of the Confederacy
Order of the Indian Wars of the United States
National Society, United States Daughters of 1812
General Society War of 1812
NSCAR - National Society, Children of the American Revolution
NSDAR - National Society, Daughters of the American Revolution
NSSAR - National Society, Sons of the American Revolution