Update: Unfortunately the amount of donations to assist those in need of help in Japan is low. For comparison purposes, the amount of donations is about 20%-50% of that of the Haiti earthquake.
Reference: http://www.washingtonpost.com/local/donations-to-japan-lag-behind-those-for-katrina-haiti-/2011/03/17/ABWzt2n_story.html
Google has created a site for worldwide crisis. The link for the Japan earthquake is here:
http://www.google.com/crisisresponse/japanquake2011.html
This page also includes charities to which you can donate. From my understanding, the Japanese Red Cross (or any charity local to Japan) would be the fastest way to get your donation to help those in Japan the quickest. Other organizations would then need to transfer funds, plus if they are providing supplies, get the supplies to Japan, whereas the Japanese Red Cross would be able to put the money to use immediately.
Update: The Japanese Red Cross organization is not a recognized charitable organization by the IRS, so contributions would not be considered tax deductible.
I know everyone has already seen terrible photos and videos of the earthquake and tsunami. For those who are interested, I thought I would share the ones which I thought really demonstrated the devastation.
The first one show satellite photos before and after the tsunami. The bar in the middle separates before and after. You can’t see the same spot before and after at the same time. You can move the bar back and forth, though, in order to see the same spot before and after. You can either drag the bar or just click anywhere on the photo (left or right of the bar) and and the bar will automatically move to that point.
http://www.nytimes.com/interactive/2011/03/13/world/asia/satellite-photos-japan-before-and-after-tsunami.html
This one from MSNBC will show video after video, so you can stop at any time.
http://www.msnbc.msn.com/id/21134540/vp/42071883#42071883
This video is a street level view of the tsunami devastating at town.
http://www.youtube.com/watch?v=ijuwl1Zw7s0
(Replaced link with a video of better quality.)
Another video showing how quickly the water devastated everything in its path:
http://www.youtube.com/watch?v=_b-2iByqHVI
This video shows a Tokyo skyscraper swaying back and forth because of the earthquake. As you may know, Tokyo skyscrapers are built to sway. I’ve heard people feeling seasick, and you can see why.
http://www.youtube.com/watch?v=JhJzdtzl6KY
And while I know people do not want to be reminded of horrifying events, I want to keep track of some of the horrific pictures just as a reminder of how devastating the earthquake and tsunami were:

