As more and more horrible pictures documenting the humanitarian crisis in Yemen emerge I thought I'd repost this list of possible international organizations to donate to. The original post is from July 2011 and I have updated some of the info and the links.
CARE International has been active in Yemen since 1993. At the heart of its work are poverty reduction and the promotion of social justice with a focus on women's literacy, water management, capacity building of local organizations, natural resource management, and relief assistance to refugees. Next to these long-term programs, CARE also offers emergency relief to internally displaced persons (IDPs) in Yemen. From what I understand, you cannot donate directly to Yemen, but can help support the Rapid Response Fund (from which humanitarian relief in the current Yemen crisis is funded) here.
The International Committee of the Red Cross in Yemen is active in a number of fields in the country, amongst which are support to IDPs in Yemen due to the conflicts in North and South as well as refugees and asylum seekers in Yemen, support for detainees in Yemen prisons and vocational training for women prisoners to support social reintegration as well as advocacy for humanitarian principles. You can donate to the Red Cross in Yemen under "other operations" on this page.
Oxfam has been active in Yemen for about 25 years. At the core of its work in the country is advocacy for greater justice for women in Yemen, which includes campaigning against early marriage, increasing women’s economic empowerment, access to healthcare in remote villages, and working to secure legal protection. In regard to disaster preparedness, Oxfam cooperates with the Yemeni Red Crescent. You can donate directly to the 'Yemen crisis' here.
The World Food Programme (WFP) in Yemen focuses on food assistance to the most vulnerable. It has been active in Yemen since 1967 and has in recent years added several special programs to this broader aim, amongst which are emergency assistance to families affected by the conflict in Sa'dah, relief and recovery assistance to refugees from the Horn of Africa, and food for girl's education. You can learn more about the WFP's activities in Yemen here and there's a 'Donate'-button on the upper right side of the page if you want to contribute. It seems impossible, though, to donate to Yemen directly.