Internet Phone Connections (9780078822698): Cheryl Kirk This reference was used mostly to teach from during my "VoIP Entrepreneur" hobby.
Introduction to Computers and Information Systems, Robert A. Szymanski, This is a beautiful, covering computing from it's beginnings. It's almost an encyclopedia of computing.
ABC Flow Charter I thought this software at Kraft Foods. It was fun learning to calculate costs based on the Flow chart.
