Being as I'm old and never throw away or sell my game systems, my collection seem crazy large. I wish I had an entertainment center large enough to hold them all and that my cats didn't like chewing on cables so I could keep them all out. I have:

Sears Telestar (that only plays Pong type games)

Atari 2600
Atari 5200

Sega Genesis
Sega Saturn (Japan)
Sega Dreamcast (USA)
Sega Dreamcast (Japan)

NES
Super Famicom (Japanese SNES)
GameCube (with Gameboy adapter)
Wii

Gameboy (antique B&W 4 battery version)
Gameboy Color
Gameboy Advance
Nintendo DSi

Neo Geo CD (Japan)
Neo Geo Pocket Color (USA)

Bandai Wonder Swan

X-Box (original on permanent loan)

As for systems I'd like to add to my collection I want a Vectrex, 3DO, Nintendo Virtual Boy and an Atari 7800.