Like julia_here said. I despise the chip and find it much more fun to write Spike without it, so, let's see... 'Notice' has him getting accidentally electrocuted in a fight and it's toast. 'Sweeter Far Than Flowing Honey' has Rack killing it. 'Compass Rose' has Drucilla making a glamor that 'fools' it and basically it doesn't work anymore since no one is human to it anymore. 'Credence' has it being fried 'cause the Initiative is going down and, you know, explosions and etc. and it was being tinkered with... Had one with an MRI machine being used but - a computer chip wouldn't actually be affected by a magnet since it has no magnetic storage on it, so that was a mess-up on my part.

If you want the stories at all, they're all on my site.
:)

I've also read Vamp!Xander hooking him up to a car battery and in a Te story it seems maybe Dru dug it out - it's never really made clear. Also lightening has fried it. I don't have links to those stories, unfortunately.