Earlier this month Ionut discovered that Google Docs offers an undocumented feature that lets you embed PDF files and PowerPoint presentations in a web page.

http://googlesystem.blogspot.com/2009/09/embeddable-google-document-viewer.html
http://blogoscoped.com/forum/160092.html

Now Google 'officially' launched this feature and created a page where the embed code can be created. http://docs.google.com/viewer

http://googledocs.blogspot.com/2009/09/view-online-files-using-google-docs.html