The first link on the left allows a "personal" search that privileges a number of HoST websites. Feel free to suggest other sites you think relevant for the HoST community.
The second link gives you access to Google Scholar, "a simple way to broadly search for scholarly literature. From one place, you can search across many disciplines and sources: peer-reviewed papers, theses, books, abstracts and articles, from academic publishers, professional societies, preprint repositories, universities and other scholarly organizations."Google Scholar ranks "articles the way researchers do, weighing the full text of each article, the author, the publication in which the article appears, and how often the piece has been cited in other scholarly literature. The most relevant results will always appear on the first page." The citations are linked too, showing interesting threads. You can add the full citation of a result on Google Scholar to your bibliography manager: visit the Scholar Preferences page and select your preferred citation format in the "Bibliography Manager" section. Scholar currently support RefWorks, RefMan, EndNote, and BibTeX. Once you've saved your preferences, you can import a citation by clicking on the appropriate link in your Google Scholar search results.
The third link gives you access to Google Book Search. You can
"Search the full text of books to find ones that interest you and learn where to buy or borrow them. Just do a search on Google Book Search or on Google.com. When we find a book whose content contains a match for your search terms, we'll link to it in your search results. Click a book title and you'll see, like a card catalog entry, some basic information about the book. You may also see a few snippets of text from the book showing your search term in context. If the publisher or author has given us permission through our Partner Program then you'll see a few full pages from the book and if the book is out of copyright, you'll be able to page through the entire book. In all cases, you'll see links that lead directly to online bookstores where you can buy the book."
The fourth link connects to Gallica, la bibliothèque numerique de la Bibliothèque nationale de France. "Gallica propose un accès à 90 000 ouvrages numérisés (fascicules de presse compris), à plus de 80 000 images et à plusieurs dizaines d'heures de ressources sonores. Cet ensemble constitue l'une des plus importantes bibliothèques numériques accessibles gratuitement sur l'Internet."