The question how you find, view, preview, collaborate, and work on your documents in SharePoint. A configurable solution designed exclusively for SharePoint providing fast viewing and document thumbnails. http://www.vizit.com/learn
An other solution from Xavier Vanneste (MVP) : http://blog.xvanneste.com/Documents/Documents/Forms/AllItems.aspx
This project extends the features of SharePoint 2010 and the Office Web Apps allowing to display thumbnails of all of the SharePoint Portal document.
See the docs and go on Codeplex