Vital Records
Vital (birth, marriage, death) records are housed at the state or local level and are thus more difficult to find than the national-level census. Also they have been recorded for varying lengths of time, depending on the state. That said, they've long been considered the core of genealogy, since they're the official records of an individual's existence.
Many are available in Ancestry. The state links on the USGenWeb Project page will lead you to other sources. RootsWeb is also a source for vital records.
The Family History Library in Salt Lake City has many vital records indexes on microfilm which can be obtained via one of their local Family History Centers. If a record for the same source occurs in WorldCat, our Interlibrary Loan Department can get it. Put the OCLC No. (found at the bottom of the WorldCat screen) in the OCLC field on the Interlibrary Loan request.
VitalChek Express is a commercial service for obtaining vital records documents
Massachusetts Vital Records (1841-1910) Index
Obituaries are not an official record of a person's life but often include vital dates and other clues to a person's life.