With USENET: Netnews for Everyone Fristrup has tried to spread the good news as widely as possible; her book is an introduction aimed at the complete novice to the net. It begins with a 40 page introduction which provides a very brief description of what USENET is and how it works and (thank God!) gives a minimum set of netiquette rules. This is followed by 200 pages listing all the groups (and accompanying FAQs) in the main hierarchies. (The book appears to have been written a year ago, so this is out of date, but it will still give newcomers some idea of what's available and where to look for things.) The third section explains how to go about getting USENET access and mentions some of the other tools around (ftp, gopher, WWW, etc.). The appendices contain some of the well known pieces on USENET (mostly Gene Spafford's work), a list of all the alt newsgroups (really out of date by now!), some stuff about newsreaders and suggestions for further reading.
I'm not sure the price tag on Netnews for Everyone is really justifiable — an awful lot of it was presumably either machine generated or just copied — and I haven't really looked at alternatives, but it's readable and seems to cover all the essentials. I won't have any qualms about passing it on to my users.