These are the simplest books on PIC programming referenced here. Also see others below. Written as a text for a course in engineering design, this is a very useful compendium on mechanical and electronic construction techniques, lots of practical tips and homebrew sensors. An excellent book that goes into detail on a great many sensors, from simple to very complex. An excellent reference book.
Some parts are highly technical.
A book on mobile robot control methodologies, covering many different control concepts. A detailed examination without going into specific languages or mathematics. A rich source of ideas for controlling the action of your robot. Case studies of working robots in the areas of mapping and navigation, vision and mobile robot architectures. Some chapters are easy to read, but mostly this is an intermediate-reading level.