Census-Online.com - census transcriptions for  Marion Co.
Marion County, Marriage Database
Marion County, SC GenWeb Project collection of online resources for genealogy researchers
Marion Co. Genealogy Forum read and post messages about your ancestors for this county
Pee Dee Chapter of the SC Genealogical Society
US GenWeb Archives for Marion County cemeteries, newspapers, wills, military rosters etc recorded online
World War II Honor List of Dead and Missing Army and Army Air Forces Personnel - Marion County page 1 and page 2

Additional Resources

South Carolina Newspaper Search enter your ancestor's name to instantly search the world's largest newspaper archive; over 12 million newspaper pages
South Carolina Birth Records
South Carolina Marriage Records
South Carolina Divorce Records
South Carolina Death Records