Creating .XLS and .XLSX with C#

Code samples:
Visual Studio 2008 C# ASP.NET MVC Web Application
http://sites.google.com/site/leniel/blog/ExcelWriterMvcProject.zip

References:
ExcelPackage: Office Open XML Format file creation
http://excelpackage.codeplex.com/

ExcelPackage binaries download
http://excelpackage.codeplex.com/Release/ProjectReleases.aspx

NPOI
http://npoi.codeplex.com/