There's a site (http://www.edrugsearch.com/hc100/index.php ) I peruse from time to time that has the "Top 100 Healthcare Blogs." My favorite is the New York Times Health Blog (http://well.blogs.nytimes.com/ ). I find the minimalist design appealing (e.g. simple black font on a white background) and the photos engaging.
The layout of the blog is consistent with my expectations: daily content on the left and semi-permanent content on the right. The consistency makes the blog visually appealing because I don't have to spend time on figuring out what I'm looking at or how to navigate it. The blog usually only has one or two advertisements that are not health related; this is appealing because I don't have to spend time on looking/reading unrelated content. FYI: an unappealing blog http://www.badscience.net/