I've lost count long ago. Probably many more than 15.

about 4 i only got the ones that are useful lol

Too many music game peripherals.

4 GBA/GCN link cables

component, composite, and s-video cables of all kinds.

I spend too much on video games.

For my PS3:
1) Jabra Headset
2) Hory fighting stick to play SF4
3) Rockband Guitar, Microphone and drums - got it for cheap
4) GH3 Guitar - got it for cheap

So 6 totally
Additinall DS3 is not included

Just a bluetooth headset

Wasn't completely sure what my answer should be but I went for 1-3. However if you count each buzz controller separately and each singstar microphone separately then I have 7 accessories. But since you can only buy buzz contollers in sets of 4 and microphones come in 2's I considered the set as a single accessory.

too many to remember and too many to list , i suck at keeping collection so i just rack stuff in the basement only shadow of the colossus i keep in my room thats how much i love the game.

edit : yes i know SoTC is not an accessory but my old gen accessories are in the basement only the new ones are kept in my room for space ... i am thinking of selling stuff...

For my PC I got:
A meh Creative gamepad I never use
A 3 axes joystick
A wheel with pedals
A gaming pad that ergonomically maps the most used keyboard keys.

Plus an older meh wheel of which a very flimsy gear pad broke and an old MS joystick that I liked very much, but it broke two weeks after the warranty expired.