These have been gathered from the internets and are locally mirrored for my reference.
DBX Tutorial -- By Drew Johnson from mathcs.carleton.edu
DBX(AIX) & XDB(HPUX) Tutorial -- By Olof Barring from CERN.ch
DBX Command Reference Guide (Shortend man page) -- By Erik Cabetas
DBX on IRIX (detailed examples and howto) -- By SGI (orginal)
GDB Reference Guide (two pages condensed) -- By Roland H. Pesch from gnu.org
GDB Reference Guide (six pages uncondensed) -- By Roland H. Pesch from gnu.org
GDB Essential Commands -- By cs.cmu.edu (original)
Tips on Using GDB with Objective C -- By Crawford/Seidel from stanford.edu
WINDBG Cheat Sheet -- By Richard Johnson
OpenVMS Debugger-- By Anthony S. Pyzdrowski (California University of Pennsylvania)