Medstory is a new search engine, still in beta, that offers "Intelligent Search for Health & Medicine." The features are really interesting -- I did a search on "melanoma," and at the top of your results you'll find "Information that Matters" -- specific categories of information regarding melanoma, including Drugs and Substances, Conditions, Procedures, In Clinical Studies, Complementary Medicine, Personal Health, and People. Each of these categories has five related topics, and you can click on any of these to narrow your search to that topic, or include that term in your original search query.
Beneath these categories are the Web results -- but even here you can narrow your results to specific types of information -- news, audio/video, clinical trials, or research articles. You can even subscribe to an RSS feed for each search.
I love these types of search engines, because nowadays I think search is all about narrowing down your query to more easily digestible chunks -- and Medstory does a good job of that, I think.