This is what I found from quickly looking, some of the more obscure systems are proving hard to find numbers for. (* I added more from oliist's number below and from Riot Of The Blood numbers above).
Generation #6
PS2 - (Still Pending)
Xbox - 25,000,000
GC - 21,000,000
DC - 10.6 Million
Generation #5
PS - 102.49 Million
N64 - 32.93 Million
Saturn - 9.5 Million
3DO - 2 Million
Jaguar - 0.25 Million
Amiga CD32 - <0.1 Million
PipPin - 0.042 Million
PC-FX - ????
Playdia - ????
LaserActive - ????
FM Towns Marty - ????
Generation #4
SNES - 49.08 Million
Genesis - 30.75 Million
TBX-16 - 10 Million
Mega/Sega CD - 6 Million
NeoGeo - 1 Million
CD-I - 0.57 Million
Amiga CD-TV - ????
GX4000 - ????
Generation #3
NES - >60 Million
C64 Game System - 30 Million
Master System - 13 Million
Atari - 7800 - 2-3 Million
Generation #2
Atari 2600 - 30 Million
Colecovision - >6 Million
Intellivision - >3 Million
Generation #1
Magnavox Odyssey - <0.34 million first Generation
