I've recently read Alan Weisman's "World without US", a book about what will happen to the earth with no people. I found the book when I was travelling in Europe this summer through Scientific American - there was an article with some very interesting graphics of what a fallen earth would look like. If you haven't read the book, I would highly recommend it - I mailed it out to a good friend of mine in Europe, so its one of the few books I have actually mailed out to mate!
Here is a link to the video from the site:
The History channel is also showing "Life without People", not sure if its inspired by Weisman or not, but here is the video link:
The following animation shows the deterioration of a house after humans are gone: