If you buy technical books or videos (computer programming, business, using Microsoft/Apple products, etc), you may want to check out O'Reilly's Deal of the Day. Today only, you can use coupon code DDJPN during checkout to get 50% off ebooks and videos and all revenues after author royalties will go to the Japanese Red Cross Society. So far, they have raised $40,000 and hope to reach $200,000.
If you just want to donate to disaster relief, you can do so on the Amazon website and the entire amount will go to the American Red Cross (donations over $250 will get receipts for tax purposes). But, if you need a few technical books, today's deal at O'Reilly lets you get them at half price and a portion will go directly to Japan (the American Red Cross fund is for future disasters, with the amount they direct to Japan coming out of past contributions).