Two Dimensional array to Excel Spreadsheet

If you want to write Excel file in C# try Excel Jetcell .NET component.
http://www.devtriogroup/ExcelJetcell
 
It read write excel XLSX XLS files. Very easy in use API function set + C# examples.
See C# code to write an array to Excel file:
using DTG.Spreadsheet;
...
ExcelWorkbook Wbook = new ExcelWorkbook();
Wbook.Worksheets.Add("Excelarray");
for (int i = 0; i < 10; i++)
   for (int j = 0; j < 10; j++)
   {
      Wbook.Worksheet[0].Cells[i,j].Value = arr[i,j];
   }
Wbook.WriteXLSX(@"ExcelSpreadsheet.xlsx");

You can do this using Spire.XLS just one line of code. call method insertarray,

http://www.e-iceblue.com/Introduce/excel-for-net-introduce.html

You can do that with something called Excel automation, more info here:
http://support.microsoft.com/kb/302084

Or you could use gembox.spreadsheet which is faster (266 times faster), easier to use and just better:
http://www.gemboxsoftware.com/GBSpreadsheet.htm