New and Deleted Commands and System Variables are now documented in great detail by Lee Ambrosius of HyperPics http://www.hyperpics.com.

Brief listing of AutoCAD 2007 Command and System Variable changes Here

Brief listing of AutoCAD 2006 Command and System Variable changes Here

AutoCAD 2006 reference documents from Hyperpics.com:
AutoCAD Quick Guide Reference

AutoCAD 2005 reference documents from Hyperpics.com:
AutoCAD Quick Guide Reference
System Variables Quick Guide
System Variables General Overview
Environment Variables Quick Guide
Environment Variables General Overview
Command Quick Guide

AutoCAD 2004/2005/2006 version of the old Express Tool DBView.ARX Click Here 98Kb
This tool if used improperly can cause a drawing file to get corrupted.