ASP.NET

public static string DataSetToJSON(DataSet ds)
{
    string JSON = "{\"Tables\": [";

    for (int i = 0; i < ds.Tables.Count; i++)
    {
        string tmp = DataTableToJSON(ds, "Rows", i);

        JSON += tmp;

        if (i < ds.Tables.Count - 1)
        {
            JSON += " , ";
        }
    }

    JSON += "]}";

    return JSON;
}

        public static string DataTableToJSON(DataSet ds, string dsName, int table)
{
    string JSON = "{\"" + dsName + "\" : [";
    for (int i = 0; i < ds.Tables[table].Rows.Count; i++)
    {
        //add the row JSON bits...
        JSON += "{";

        for (int j = 0; j < ds.Tables[table].Rows[i].Table.Columns.Count; j++)
        {
            string columnName = ds.Tables[table].Rows[i].Table.Columns[j].ColumnName;
            string columnValue = ds.Tables[table].Rows[i][j].ToString();

            //Replace any crlf's in the column value...
            columnValue = columnValue.Replace("\r\n", ", ");


            JSON += "\"" + columnName + "\": \"" + columnValue + "\"";

            if (j != ds.Tables[table].Rows[i].Table.Columns.Count - 1)
            {
                JSON += " , ";
            }
        }

        JSON += "}";
        if (i != ds.Tables[table].Rows.Count - 1)
        {
            JSON += " , ";
        }

    }
    JSON += "]";
    JSON += "}";

    return JSON;
}