When my first video card died... wait... the first video card I had that died... yeah thats better. Anyway. It started turning everything into multicolored negative images. Like the negative of a photo, but looking like the bottom of a bad 80's skateboard... all neon pink and green and white. It was overheating, and I didn't know it at the time. I continued to do things with it, just thinking it was graphics glitches, but soon after, I couldn't get any image at all.
My last card that died happened to be a $600+ card. An EVGA geForce 8800 Ultra KO Edition, not long after they came out with them. Lightning storm. Even through a surge protector it fried the cable modem, my motherboard, and the graphics card. The PSU and the CPU were both fine though, which actually had me laughing a little.