This includes portables and more than one of the same system. I've owned 4 systems altogether.

ColecoVision
NES
N64
Sega Game Gear
GameBoy
Gameboy Color x2
Gameboy Advance
Gameboy Advance SP x2
GameCube
Nintendo DS x2
Nintendo DS Lite
Xbox (Original)
Wii

16 in total.

N64
Gamecube
Game Boy
Game Boy Advance (x2)
Game Boy Advance SP (x3)
DS Lite (x2)
DSi (Don't have it yet, i'll get it for my b-day)

11 in total.

Nintendo 64
Game Boy Advance
Game Boy Advance SP
DS Lite (x4)
DS Phat
Wii
Xbox 360
Original Xbox

11 in total.

I used to own a Dreamcast. But it broke So counting all of my systems I have 12 Counting the ones that still work 11.

I have owned the following systems myself;

Nintendo
Super Nintendo
Gamecube (Purple)
Wii (White)
Sega Genesis
Sega Dreamcast
Playstation
Playstation 2 (Black)
Playstation 3 (Black)
GameBoyColor x2 (Blue) (Green)
Tommy Hilfiger Edition GameBoyColor
GameBoyAdvance x2 (Arctic) ( the one you can see through the surface of )
GameBoyAdvance SP (Colbalt)
Anniversity Edition GameBoy Micro
NintendoDS (Default Color)
NintendoDS Lite (Crimson on Black)

So far I have owned 18 systems/consoles total... lot of GB action due to untrustworthy step-siblings...

Under these curcumstances, I would have 19 systems including computer games & of course 18 games otherwise.

NES (7)
SNES (4)
N64 (2)
Gamecube
Wii
Gameboy (2)
GBA (3)
DSi
Master System
Genesis (3)
Sega CD
Sega Saturn
Dreamcast
Gamegear (4)
Atari 2600
Neo Geo Pocket Color
PS1 (5)
PS2
360

Total: 41

N64 (x1)
Game Boy Advance (x1)
Game Boy SP (x1)
Nintendo DS (x7 (I'm a little harsh on my handhelds))
Gamecube (x1)
Nintendo Wii (x1)
Laptop (x2)
Xavix (x1) (Anyone remember that?)

Yep, I'm pretty light on the gaming systems. Total: 15

I have, and a bit of detail behind them:

Sega Mega Drive - bought of my cousin along with the game Zero the Kamikaze Squirrel <3
Gameboy Pocket - birthday present along with Dr. Mario and Star Wars, lol
Gameboy Color - christmas present, color berry --- one of the first Color games I played was Conker's Pocket Tales
Playstation 1 - received from my auntie for my birthday along with Wild 9 and some other non-interesting games --- Wild 9 was fun
Gameboy Advanced - sold some games and bought along with Sapphire
Playstation 2 - saved up and bought at a decent price thanks to my cousin --- Kingdom Hearts/FFX-2/Metal Gear Solid 3 were the first games I got
Gamecube - it was cheap so I bought it along with Pokemon Colosseum (big mistake) --- but I got a pre-used game of SSBM so it was worth it in the end
Gameboy Advanced SP - I got it so I could trade pokemon with myself :(
Nintendo 64 - bought at a pre-used store, I used to have loads of fun playing my friend's N64 --- got it along with Donkey Kong 64/Banjo Kazooie/Mario Golf, though I wish I had Bad Fur Day or something
Nintendo DS - bought it for the new Pokemon game, obviously
Playstation 3 - I needed one for one of my favourite series, Metal Gear's last game --- also for the Final Fantasy games that are coming out fairly soon
Nintendo Wii - everyone was getting a Wii, so I got it with the soul-purpose of playing Super Smash Bros. Brawl --- other than that I hardly use it unless playing another one at someone else's house

So I guess that makes 12. I want to get a PSP next I think.

Let's see..

PS3
DS Lite
PSP (the original)
GameBoy Color, Advance, and SP
Sega Genesis
PS2 Slim
iPod Touch if you count that
Game Cube

I also used to have an Xbox 360, but it got the red ring of death or what ever it's called. Hence, I got a PS3.. and I like it a lot more. That's the only system I regularly play, and I play DS every few days to check up on my Animal Crossing town.

Atari 2600
Super Nintendo
Nintendo 64
Playstation
Playstation 2

Gameboy
Gameboy Color
Gameboy SP
DS Lite

Turbografix
N64
GBC
Gamecube
GBA
PS2
WII
DS original
PS3
Gaming PC