ExcelXMLWriter
As Steve already mentioned, we are working on generation of Excel files this week. After doing some research, I found a free ExcelXMLWriter by Carlos Aguilar. It is written in C#, and does not require Excel to be installed in order to generate the files. We played around with it for a few days, it seems to do what we want. Carlos also offers a code generator tool that transforms Excel file into C# code.
