Debuggers, tracers and codes used to access unused music for ripping into VGMs. Requesting a sticky for this... or not since the VGM ripping tutorial covers basic elements of Sega Genesis hacking. Here is a small list of powerful (and only?) Sega Genesis debuggers/Tracers/Tools for hacking games for VGM ripping.
Debuggers:
Geiger/FCUEUXDSP style debugger
http://aamirm.hacking-cult.org/www/regen.html
MAME style debugger
HazeMD
http://mamedev.emulab.it/haze/
Tracers:
Gens Tracer:
http://www.romhacking.net/utils/337/