I have a special interest in Mississippi genealogy because my father was born and raised here.
Free
The Ancestor Hunt: Free Online Mississippi Collections
There are 24 categories of records across many databases (birth/marriage/death, probate, military, and more).
Mississippi Department of Archives and History
A government website of digital and physical records related to Mississippi history and genealogy.
Mississippi Genealogy NEW!
A website with Mississippi genealogical and historical information, especially sources for records.
Mississippi State University: Archives and Special Collections
Digital and physical records related to Mississippi history and genealogy. The library can be contacted for help accessing non-digital resources. Here is the page for genealogy records by county.
Random Acts of Genealogical Kindness: Mississippi Archives, Societies & Publications NEW!
A good list of archives, genealogical societies, libraries, museums, etc. in Mississippi.