Digital Quake Relief
The earthquake and tsunami in Japan last month was the biggest disaster to hit a major city in the digital age, and many responses have been appropriately cutting edge.
Apple quickly enabled donations to the Red Cross via iTunes, as did PayPal and Amazon. Groupon was probably the first company to announce a combined contribution and fundraising campaign. It promised to match donations up to the value of 100 million yen (it hit that number), getting a huge amount of publicity via Twitter in the process.