Today, Autodesk released (see this press release) Autodesk Seek, a groundbreaking web service that allows architects, engineers and designers to search, select and specify building products using Autodesk’s advanced search technology. The technology has already been integrated into the 2009 products. If you haven't seen 2009 or maybe just haven't looked at the toolbars closely, there is a new toolbar for the Content Search.
Just type in what you are looking for (example; I was looking to see if Marvin had windows available, so I typed in Marvin) and as long as you are connected to the Internet, it will open up a browser and show you the results. It has quite a few file types you can search for, just take a look at the image below to see the types of files you can search for...
As the press release mentioned, the amount of content will continue to grow. I can only imagine how big of a database this is going to grow to!
Also, if you don't want to open up a piece of software, you can go directly to http://seek.autodesk.com/ to search for content.