Because of the vastness of this topic, I have not included other records that would confirm a birth, marriage or death date such as burial records or christening records. The web sites mentioned here are not the only ones with vital record information, they are just a sampling.
Also, you may find duplication here. In some cases records made available through Family Search Labs and through the state archives or Ancestry.com are duplicates of each other. I have decided to include these duplications because in some cases you may be able to find an ancestor in one of the web sites but not in another. Leland Meitzler, editor of Everton's Genealogical Helper, discussed this recently in his Genealogy Blog. He was able to find an aunt in the Family Search Labs transcription of the Washington State Death Certificates, but hadn't found it in microfilm versions or in Ancestry's version. So it always pays to check multiple copies.
Government Agencies and Universities
• Arizona @ http://genealogy.az.gov/
• Georgia @ http://content.sos.state.ga.us/cdm4/gadeaths.php
• Kentucky @ http://ukcc.uky.edu/vitalrec/
• Massachusetts @ http://www.sec.state.ma.us/vitalrecordssearch/VitalRecordsSearch.aspx
• Ohio @ http://www.ohiohistory.org/
• Utah State Archives @ http://www.archives.state.ut.us/main/
• West Virginia @ http://www.wvculture.org/vrr/va_select.aspx
Ancestry has vital records or indexes for the following states or parts of states:
Alabama, Arizona, Arkansas, California, Connecticut, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, New Jersey, Ohio, Maine, Maryland, Massachusetts, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Jersey, New Mexico, New York, North Carolina, Oregon, Pennsylvania, Rhode Island, South Carolina, Tennessee, Texas, South Dakota, Utah, Vermont, Virginia, Washington, and West Virginia.
To peruse Ancestry's collection of records for your state of interest, go to Ancestry's website at http://www.ancestry.com/ and then click on the ‘Search' tab. From the Search page click on the United States Map or on the list of states. To keep abreast of Ancestry's addition to its collections, check out the Ancestry Blog or its blog for Ancestry Weekly Journal
Family Search Labs
You can also view vital records that are being indexed and digitized by the Family History Library through its Family Search, http://www.familysearch.org/ website. Click on the link to the right that says U. S. and U.K. census on the Family Search homepage and it will take you to the digitized images.
Death records indexed include:
• Georgia Deaths, 1914-1927
• Ontario Deaths, 1869-1947
• Utah, Salt Lake County Death Records 1908-1949
• Ohio Deaths, 1908-1953
• Utah Death Certificates, 1904-1956
• Washington Death Certificates, 1907-1960
• West Virginia Deaths, 1853-1970
• Texas Deaths, 1890-1976
• Texas Death Index, 1964-1998
Marriage records indexed include:
• Cheshire, Church of England Marriage Records, 1538-1907
• Freedman's Bureau Virginia Marriage Records, 1815-1866
Upcoming indexing projects will include marriage records from Wales, Ireland, Philadelphia, Arkansas, and Indiana. To learn more about upcoming indexing projects through the Family History Library and in cooperation with other agencies, see the Family Search Indexing website.
Rootsweb, has a few vital records indexes, including ones for California, Kentucky, Maine, Texas. In addition, it has transcribed vital records for parts of Alabama, Arizona, Arkansas, Connecticut, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Hampshire, New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, South Dakota, Tennessee, Utah, Vermont, Virginia Washington D.C., West Virginia, and Wisconsin. To look at the previously mentioned indexes click on http://searches.rootsweb.ancestry.com/ . To look at regional resources, including the transcribed records check out the Rootsweb regional index at http://userdb.rootsweb.ancestry.com/regional.html#Us.
Overall, for a listing of various vital records online, you should consult Joe Beine's websites, Online Death Indexes and Online Birth and Marriage Records Indexes for the USA