This site is offering a newly updated version of Erik Drexlers book "Engines of Creation" for free (as an e-book). Looks like he just updated it in Feb of 2007. For anyone who hasn't read the original "Engines of Creation", I highly recommend it if you are interested in nanotechnology or are just looking for a good read. It is one of my favorite books.

Updated version of Drexlers 'Engines of Creation'