We let users create ad-hoc queries in our website. We would like to have the user select their criteria, then click submit and have the results streamed automatically to Ex
I'd recommend using a filehandler (.ashx) The only issue is creating the excel file from the DataTable. There are a lot of third party products that will do this for you (e.g. Infragistics provides a component that does just this).
One thing I highly recommend against is using the Excel interop on your server...it's very heavyweight and isn't supported.