Shazam! gave me an idea with his Sega thread when he rattled off the systems he owned. Heres mine in chronological order:
Atari 2600
Intellivision
NES
Neo-Geo (found at garage sale for $20 at the time when it retailed $400+!)
Super Nintendo
Gameboy Color
Playstation
Gameboy Advance
Playstation 2
Gameboy DS
PSP
Xbox360
Honorable Mention: Phillips CDi. Anyone remember this? It was one of the first CD drive games and had weird games like Zelda with FMV.
EDIT: Also had Nintendo Gamecube. Yes I am a fanboy, but I'll never get a Wii. That thing is too gimicky.