Depends on the level of detail your reports need to have.
A straight data extract can be done by creating a CSV file through ASP, which would map into Excel, but you won't have any special functions or formatting. It would be raw text.
If you need bar graphs and stuff, you could install a server side component to create charts and display the report as the webpage itself.
If you need complex reports with graphical capbilities, you could use Crystal Reports.