Learning the vi Editor (6th edition)

by Linda Lamb, Arnold Robbins
ISBN #1565924266, O'Reilly

The Ultimate Guide to VI and EX Text Editors

Hewlet Packard Corporation
ISBN #0-8053-4460-8, Addison-Wesley Pub Co

Vi improved (VIM)

by Steve Oualline
ISBN #0735710015, Sams (1st edition)