Here's where I stand now:
Atari
2600 (Heavy Sixer, S-video)
2600 (Vader, AV)
2600 Jr. (AV)
5200 (4-port, S-video)
7800 (S-video)
XEGS (S-video)
Commodore
Amiga 500 (modded with internal NTSC/PAL switch)
C64 (S-video)
VIC-20 (S-video)
NEC
PC Engine (S-video)
PC Engine Duo-R (RGB, modded with model 1 Genesis power jack)
TG-16 (RGB, modded with the Obey chip)
TurboExpress (modded with the Obey chip!)
Nintendo
AV Famicom (modded for Zapper compatibility)
Famicom (AV)
Famicom Disk System
Game Boy (backlit, has NES D-pad and buttons)
Game Boy Advance (white)
Game Boy Advance SP (AGS-101, black)
Game Boy Color (purple)
Game Boy Pocket (silver)
GameCube w/Game Boy Player
N64 (RGB, cart slot tabs cut)
NES (external audio mod and disabled lockout chip)
NES top loader (AV)
SNES mini (RGB and S-video, also modded with model 1 Genesis power jack, has cut tabs)
Super Famicom (cart slot cut to fit SNES games)
Sega
Japanese SMS (S-video)
Japanese Mega Drive (stereo RCA jacks, English/Japanese region switch)
Game Gear
Genesis 2 (S-video, region switches and CCAM)
Mark III (amplified RGB, FM mod coming soon)
Mega CD II (regionfree BIOS planned)
Nomad
Saturn (model 2, modchip planned)
Sony
PSX (SCPH-9001, chipped)
PS2 (chipped, has Network Adapter and 80GB hard drive)
Misc.
ColecoVision (component video, 5V power mod)
Panasonic FS-A1 (MSX2 system)
SNK Neo Geo AES (S-video, has power LED in the reset button)