The WHO have a project called International Clinical Trials Registry Platform, which includes a search engine for clinical trials, available at http://www.who.int/trialsearch/.
This searches a database containing information from a number of sources. It is not itself a clinical trials registry. I can't immediately find a list of these sources, but there may be one somewhere.
I saw mention of this resource in an email from Virginia Ballance, Hilda Bowen Library, College of the Bahamas, to the MEDLIB-L discussion list.