Here are a few resources which I’m sure some of you already know about:
@todrobbins really useful. Would you have any further info on each of these. E.g. description, size, openness.
Also see clinicaltrials.gov (fact sheet: http://www.nlm.nih.gov/pubs/factsheets/clintrial.html) – they have a pretty good API.
There is also recent(ish) legislation to require studies to publish not only enrollment status but also results – see https://clinicaltrials.gov/ct2/manage-recs/fdaaa