The World Health Organisation's International Clinical Trials Registry Platform (WHO ICTRP) is available here.
Articles about trial registration
De Angelis CD, Drazen JM, Frizelle FA, Haug C, Hoey J, Horton R, Kotzin S, Laine C, Marusic A, Overbeke AJPM, Schroeder TV, Sox HC, Van Der Weyden MB. Is this clinical trial fully registered? A statement from the International Committee of Medical Journal Editors. Lancet 2005;365:1827-1829. [Available here]
Ghersi D, Pang T. From Mexico to Mali: four years in the history of clinical trial registration. Journal of Evidence Based Medicine 2009;2:1-7. [Available here]
Hasselblatt H, Dreier G, Antes G, Schumacher M. The German Clinical Trials Register: challenges and chances of implementing a bilingual registry. Journal of Evidence-Based Medicine 2009;2:36–40.[Available here]