If you're into medical information, take a look at MedNexus, which claims to be the Google for Medicine. I can't pretend to any great medical knowledge, so please take that into account when reading this post. Their 'about us' page says: "Through our search engine, you can find the most relevant content from a variety of sources: medical journals, patient forums, government health sites, etc. We want to empower patients to educate themselves and cut through the noise and pseudo-science of typical online health information. No more WebMD scares, no more endless Googling"
MedNexus is designed for patients to use, and it provides information in a clear, concise and non threatening manner. This will doubtless be helpful to those people who have Googled their symptoms and believe that they're 5 minutes away from death. When typing in a condition such as migraine, the engine provides instant suggestions such as 'What is Migraine' 'How do you treat it?' and lifestyle tips, treatments and so on. Clicking on results will give you a very wide range of information, such as common treatments, articles, explanations, published research, and forum discussions. Information is pulled from a variety of different sources such as Healing Well, MedHelp, American Journal of Medicine, JAMA and so on.
This engine won't be of much use to medical professionals, since they have their own resources to hand of course, but it's certainly a tool that I think is worth pointing out to members of the public, who simply want to explore a medical condition in more detail, and from a reliable resource.