Currently:

PlayStation
PSOne
Genesis (AKA Mega Drive II)
Saturn
Dreamcast
PS2 (NTSC-US)
X-Box
360
N64
GameCube
Gaming PC

In the past I have owned;

PS2 (PAL)
Master System
Game Boy
Game Boy Color
DS Lite
A second PlayStation
Gaming PC (Three seperate ones, though one was technically my mother's.)

Future:

Wii
PS3

I get most of my 4th gen gaming fixes from emulation these days.