Sites that are, or Contain Lists of, Search Engines and Repositories that include Biomedical Topics:

• VADLO
  a biomedical search engine wherein queries can be restricted to protocols, online tools, seminars, databases, and software.
• DOAJ
  Directory of Open Access Journals - covers free, full text, quality controlled scientific and scholarly journals.
• Nature Precedings
  archive of pre-publication research, unpublished manuscripts, presentations, posters, technical papers, etc. in biology, medicine (except clinical trials), chemistry and earth sciences.
• Quadsearch
  metasearch engine for scientific articles. Also computes H-index for authors although it does not disambiguate author names.
• OReFiL
  allows for searching for online resources (URL's) described in scientific articles.
• PubMedCentral
  the NIH free digital archive of full-text biomedical and life sciences journal literature (much of which are open access).
• CiteSeer
  indexes PostScript and PDF research articles on the Web, focusing primarily on the literature in computer and information science.
• Rexa
  a digital library and search engine covering the computer science research literature and the people who create it.
• arXiv
  Physics E-Print Archive: mostly physics, math and computer science, but has some biomedically relevant articles (e.g. on biophysics and information retrieval), including unpublished articles and those in press.
• Cogprints E-Print Archive
  author-submitted archive for papers in any field related to cognition.
• Google Scholar
  searches literature on the web and from various publishers.
• Scirus
  searches both the literature and the web on scientific topics.
• KartOO
  web metasearch engine that displays the output in visual form and permits one to zoom in and out while refining one's query.
• Grokker
  web search engine that displays the output in visual form and permits one to zoom in and out.
• Teoma
  In contrast to Google, which ranks web pages according to how many other sites link to it over the entire web, Teoma attempts first to define small communities of webpages that are devoted to the topic covered by the query. Then, Teoma ranks webpages according to how many other sites link to it within that same topical community. Teoma also provides suggestions to limit and refine searches.
• CompletePlanet
  compendium of search engines, including U. S. Patents, Cancer Net, Census Bureau, Library of Congress, and many more on all topics.
• MediLexicon
  compendium of search engines for abbreviations, medical terms and a variety of other medically related topics (e.g., upcoming conferences).
• HONselect
  site that certifies medically related web sites for objectivity.
• SUM Search
  site for clinical queries, similar but not identical to PubMed clinical queries.