Xbox 360 Red Ring of Death
There I was, playing a little Marvel: Ultimate Alliance, when the Xbox locked up on me while loading the next level. It's happened before, so I turned the Xbox off (the control was unresponsive after several minutes) and turned it back on again.
And I saw the Red Ring of Death.
Apparently this is common enough to have a knowledge base article all to itself.
This is actually the second Xbox 360 I'll have had - my last one failed on my birthday last July. Different failure, but both times I've had to send it back to be fixed. Hopefully I won't have to go through the DRM hoops I had to go through last time to get my Xbox Live Arcade games to work on whatever console comes back to me.