Worst bug monetarily:

I was consulting for a multinational on a commodities trading app. I broke the stuff sending trade data to the Risk Management system that does automatic hedge trades. My manager comes down the hall and tells me I've caused $4 million in exposure in the past two hours. At the end, her comment is: "A million here, a million there, business as usual!"

I told that story to a former coworker, and he pointed out, "Well, your boss was calm about it. I bet those traders were livid!"