Médecins Sans Frontières/Doctors Without Borders is the first organization that jumps to mind -- they've been helping to lead the response in Africa, more or less on a shoestring.

Their US donation page is here: https://donate.doctorswithoutborders.org/onetime.cfm

Folks in other countries can find their local donation pages here: http://www.msf.org/donate

EDIT - To give you a sense of how involved MSF has been in the Ebola response: "Since March 2014, 14 MSF staff members have become ill, among whom 8 have sadly passed away." (Source: http://www.msf.org/article/ebola-workers-risk-tragic-reality...)

There's a comprehensive rundown of their efforts to date to help contain Ebola across West Africa here: http://www.msf.org/article/ebola-crisis-update-sept-25th

Thanks for the info, just did a small donation. I suspect it's well beyond their ability to control at this point, but even slightly slowing down that exponential curve can be worth a lot.