I've been through two big earthquakes, but I was lucky enough in both cases to live in wealthy areas that have strict building codes which were amazingly effective in minimizing deaths from building collapses. Haiti isn't so lucky, of course; it's a poor country and now with the huge earthquake, the folks there could use some extra help. Michael Leddy, who blogs at Orange Crate Art, has put up some helpful resources here.
The US State Department has a page with resources.
The Rachel Maddow show on MSNBC has a page up with links, too.
Because of my regular contact with the local blood donation center, I think of the American Red Cross for such occasions. Here's a page they have up about how they're already working to help.
There are lots of aid organizations doing good work around the world. Peace Corps is my favorite, but they're not in Haiti. Feel free to share your favorite(s), and I'll be happy to add them to this page if they seem appropriate for helping Haiti at this time.
Edited to add:
Feel free to link, of course.
LenapeGirl suggests Doctors Without Borders. Here's the link.
Susan suggests Episcopal Relief and Development. Here's the link.
Dr.GunPowderPlot suggests Oxfam America. Here's the link.