DevTopics has posted this series of famous software disasters:
Here's my favorite one:
10. Ariane Rocket Goes Boom (1996)
Cost: $500 million
Disaster: Ariane 5, Europe's newest unmanned rocket, was intentionally destroyed seconds after launch on its maiden flight. Also destroyed was its cargo of four scientific satellites to study how the Earth's magnetic field interacts with solar winds.
Cause: Shutdown occurred when the guidance computer tried to convert the sideways rocket velocity from 64-bits to a 16-bit format. The number was too big, and an overflow error resulted. When the guidance system shut down, control passed to an identical redundant unit, which also failed because it was running the same algorithm.
Mental note: when designing redundant systems for space rockets remember to disable overflow checking - if we can't guarantee the correct destination, let's guarantee that if flies for as much as it can (it cost $500 million, so let's at least lower the cost per flown mile ratio)