Sites that are the most useful in getting started
and most likely to give quick results.

Who are you looking for?
Ancestry Lots of databases of records, including all US census years. 
FamilySearch Records from original sources and submitted material.
GenForum Queries by surname. Each surname has a search.
Mailing Lists Queries. Enter a surname or get a List of surnames.
Passenger Lists Use this site for easy searching of Ellis Island or Castle Garden.
Death Indexes Online searchable death indexes & records.
Where were they?
USGenWeb County Web sites.
Mailing Lists Enter 2-digit state, followed by the first 6 digits of county.
SamPubCo Indexes of wills by county. See book number for date range.
USGS Maps Find out where a US location or cemetery is and see a map.
What else is there?
Cyndi's List Everything on the Web related to genealogy.
Your Local Library Database subscriptions: AncestryPlus, HeritageQuest, NewsBank
Military Indexes Online military indexes & records.
Sharon's Home page of my genealogy site.