If you want provide donations to the LDS Church so that they can help the people in Japan, please go to LDS Philanthropies and make a donation to the Emergency Response Fund.
The LDS Church has also released a statement about the earthquake in Japan and that most LDS missionaries serving in that area are safe and accounted for:
"Our thoughts and prayers are with the people of Japan following the recent devastating earthquake and tsunami.There has been a high volume of inquiries concerning the safety of missionaries serving in the area. The most immediate information is that five of the six missions in Japan have reported all missionaries are accounted for and safe. However, all communications systems in the Sendai area are down. We have not been able to contact each missionary in that mission yet. We continue to work diligently to account for the missionaries in this area and will update information as we are able to do so.Initial reports from missions in areas affected by tsunami activity show all missionaries are safe.We are also assessing how the Church might help meet the needs of people affected by the earthquake and tsunami."
Keep checking back here at LDS Phrontistery for more updates on the LDS Church and their involvement in helping the people of Japan.
Update #1 (3.13.11): It has been confirmed that all missionaries in Japan are safe and accounted for.