This week we have a story to add the ability to extract some of the data within our system into Excel format.  Upon initially hearing the requirement I thought of Visual Studio Tools for Office (VSTO), but after digging into the documentation for a bit, it doesn't seem that it was meant for our scenario.  VSTO seems to be ideal for Office Add-ins but quite lacking in its support for server based scenarios.

We did a bit of research and found a couple commercial options such as Software Artisans OfficeWriter and Aspose.Cells. Additionally, this evening Aaron emailed me about Carlos Aguiar's ExcelXmlWriter project that provides a free utility for generating Excel files as well as a nice generator. 

I'd certainly be interested in hearing about any other components that anyone has used for generating Excel in a server environment and/or any experiences with the products mentioned above.