What do you think are the essential books for readers of sci.space.*?

Well, it depends on one's interests, but the Isakowitz is pretty
helpful if you want to keep track of which rockets are being built
around the world. It lists payload, fuels, performance, launch sites,
and other stuff of that sort.

If you don't want to spend the $80, the
http://www.faqs.org/faqs/space/launchers/ page is pretty good (but
rather outdated, even more so than the 3rd edition of the paper
Isakowitz).

There are plenty of web sites which have some of this, for example
http://www.astronautix.com/ or
http://www.spaceandtech.com/spacedata/elvs/elvs.shtml