It seems to have slipped under most people's radar, but
there are an awful lot of scientific and technical books being
published these days that are free in electronic form. Believe it
or not, many major publishers are willing to give away a book
in electronic form while at the same time charging money
for it in bound, printed form. I run
a web site called The Assayer (http://theassayer.org) for
user-contributed book reviews, with a focus on free books.
Since I teach physics, and am the author of a free physics
textbook myself, I have a special interest in collecting
reviews of physics books. If you're interested in reviewing
free and unfree physics books, or reading reviews of them,
I invite you to check out the science section of the site: http://www.lightandmatter.com/cgi-bin/asbrowsesubject.cgi?class=Q
In particular, Warren Siegel has written a free textbook on
field theory which is a major piece of work, and I'd love
to see someone review it -- it's not easy finding someone
with the necessary theoretical knowledge and the willingness
to wade through something this dense and difficult.
I know this list also has periodic discussions along the lines
of "What do people on the list think is the best book for
(high school/algebra-based physics/engineering physics...)?"
It would be cool to organize and collect some of these thoughts
on The Assayer.
BTW, I have an obvious conflict of interest with respect to
my own book, so while I've written reviews on The Assayer of
several introductory physics texts, I've tried to avoid any
that compete with mine in the one-year physics-for-life-
science-majors type of course.