I personally chose AID India to send my money to since they have been great in disbursing the funds immediately. You can contribute to them at http://survivors.aidindia.org.
If you prefer to contribute to other organisations, here is a bunch of them:
http://www.csmonitor.com/2004/1229/p10s01-usgn.html
http://www.bapscare.org/mediacenter/announcements/2004/tsunamireliefwork.htm
https://www.aidindia.org/aidadmin/DonateToRRF.jsp
http://www.idrf.org/dynamic/modules.php?name=Hnnews&file=article&sid=157
https://www.myhelpinghands.org/tsunami.asp
http://www.ashanet.org/index.php?page=tsunami-relief
http://www.nextgenfoundation.org
http://www.providentliving.org/content/display/0,11666,5595-1-2910-1,00.html
http://www.indianredcross.org/donation.html
http://www.seedsindia.org
http://pay.hindu.com/thrfpay/thrfpay.jsp
http://www.redcross.org or call 800-HELP-NOW
http://www.americares.org or call 800-486-4357
http://www.doctors-withoutborders.org or call 888-392-0392
http://www.mercycorps.org or call 888-256-1900
http://www.savethechildren.org or call 800-728-3843
http://www.careusa.org or call 800-521-2273
Also you can check the local and online news sources for other means to help. The following blog has some additional info on the Tsunami relief efforts.
http://tsunamihelp.blogspot.com/
Just remember, you can make a difference.