GemBox.Spreadsheet is a .NET component that enables developers to
write, read or convert spreadsheet files (XLS, CSV, XLSX, HTML or ODS)
from their .NET applications using one simple API.

Some of the new features:
- Full support for OpenDocument spreadsheet (.ODS) file format - Read
and write ODS/ODF files from .NET
- XLS formula parser now supports additional 150 Excel functions
- New sample explorer

GemBox.Spreadsheet requires only .NET Framework and is many times
faster than Excel Interop/Automation object. GemBox.Spreadsheet Free
Excel component is free of charge while GemBox.Spreadsheet
Professional is a commercial version.

Examples of common uses of GemBox.Spreadsheet:
- Reading and Writing XLS, XLSX, CSV and ODS files
- Writing Reports in XLS, XLSX, CSV and ODS files
- Import or Export DataGrid, DataSet and DataTable to Excel or HTML
files
- Exporting Excel files to HTML from .NET
- Converting XLS, XLSX, CSV, HTML and ODS


http://www.gemboxsoftware.com/GBSpreadsheet.htm