Here are some books Nikto is discussed in. In no particular order.
Harry Anderson's Introduction to Nessus drops a nice line for Nikto (and nmap & Hydra), calling them the "best applications in their class".
Assessing Internet Security Risk, Part Five: Custom Web Applications Continued by Charl van der Walt makes liberal mention of Nikto as a tool to use.
Jericho pointed out that the 2004 SANS Top 20 list plugs Nikto as "one of the more comprehensive CGI scanning tools" in section U3.5.