If big consequences is what you're after, I can think of three typical incidents: the "most expensive hyphen in history" (you can search it like that), it's companion piece, the Mars Climate Orbiter(which I see you added now), and the Denver Airport Baggage System fiasco [1] where bad software planning caused over $500M in delays.

[1] http://calleam.com/WTPF/?page_id=2086