Fold3.com is a database of military records from the National Archives. (subscription based)
Ancestry.com is the most popular genealogical research site ever. (subscription based)
Rootsweb has an amazing variety of free resources for genealogy. (free)
Genealogical.com is THE place to buy genealogy books. (online store)
BLM- GLO Records – Find land patents, grants and surveys. (free)
Family History Library Catalog (FamilySearch.org) (free to search; order microfilms to be delivered to your local FHL for about $10 each)
Library of Virginia Catalog Search (free to search for existing records; some are digitized, others must be located physically in the library).
WikiTree – a fabulous online collaborative tree run by volunteers