SearchHut
I like the idea of searching a curated list of domains, but I'm not sure that doing the curation yourself is the best approach considering the huge number of useful but niche websites in existence.I wonder if simply parsing all of Wikipedia (dumps are available, and so are parsers capable of handling them) and building a list of all domains used in external links would do the trick. Wikipedia already has substantial quality control mechanisms, and the resulting list should be essentially free of blog spam and other low-quality content. Wikipedia also maintains "official website" links for many topics, which can be obtained by parsing the infobox from the article.