Datamining with Office 2007
This is an awesome add-in and best part is it comes free with Office 2007. This gives two extensions with Excel (Analyze and Datamining tabs) and one extension to Visio. I just was playing around with this and this is awesome. We can do some of the Data Mining stuff of SQL Server 2005 just out-of-the-box using Excel spreadsheets.
Download the same here.