Below you will find a rather eclectic list of sites with descriptions that are some of the more useful tools to find a variety of specific information like reference sites, search tools for other countries, and more. This is a category for excellent sites that did not fit into the other groups, yet certainly merited inclusion.
Google Book Search is a cooperative project between Google and several major libraries from the United States and other countries. The intent is to digitize books that are out of copyright and allow limited previews of copyright books. The previews will often provide access to the title page, the table of contents, the index, and snippets that contain a few sentences using the search terms in context. A Google Book search can retrieve information from chapters or sections of books--information that cannot typically be found in a library catalog record. Using Google Book Search to find more information about a book held in a library or to search inside the content of a book can be an indispensible tool for locating information that was often hidden.
Google Scholar searches for scholarly academic information from articles, theses, books, digital collections, and more. It is particularly useful when configured to find full text in a library in which you have access to the collection. You can configure Google Scholar in the Preferences to link to sources available in your library. One word of caution is Google has yet to use publication date as a factor in relevancy, so you may want to click the Advanced Search to limit the date to articles published more currently.
USA.gov is the official portal to United States government information including Web sites, citations, and other useful links.
Wikipedia is an open content, free encyclopedia with multilingual articles that are collaboratively developed and edited by anyone covering a wide range of topics. Wikipedia has grown into an excellent resource for find basic information about a topic. Perhaps, it may not be the Britannica yet, but it is certainly more current and useful as a general source for helping understand a topic before beginning in-depth research.
How Stuff Works explains everything from Boolean logic to nuclear energy to car engines, stocks, and finances. This site provides good answers to the questions of how a various things work. One of the more fun and informative pages on the Web!
Microsoft Academic Search is Microsoft's free scholarly search engine that functions similarly to Google Scholar but seems to no longer update the database since about 2011. This nearly makes this resource unusable. That said, perhaps there will be some improvements in the future.
The LibrarySpot is a collection of Web sites that is organized like a library. A reference section, reading room, special collections, must-see sites, and more provide resources to from everything to electronic journals and newspapers to top colleges, foundations, quotations, genealogy, and more. A site that is well-worth the visit.
Although the list of resources here is a bit cumbersome, Refdesk.com offers a host of sites that are useful for finding information. To quote the mission statement, "Refdesk.com has three goals: (1) fast access, (2) intuitive and easy navigation and (3) comprehensive content, rationally indexed. The prevailing philosophy here is: simplicity. 'Simplicity is the natural result of profound thought.
EL.com is a destination site that offers a variety of information from reference, newspapers, and search tools to money, shopping, and more. Although much more commercial than any of the subject directories, EL provides links to some excellent resources and as such is an excellent portal site.
MagPortal.com offers access to searchable database of selected full-text magazine articles available on the Web. Although MagPortal.com contains a limited selection of magazines from the recent couple years, it is worth trying when searching for articles.
Search Engine Colossus is a comprehensive directory of search tools that is international in scope and currently has 882 listings. The links are organized by country with some subject categories. A scrolling script provides a series of @This and That information about search tools. This is an excellent source for international search tools.
HotSheet is more than just a metasearch tool. Actually, the best part of HotSheet is the difficult to navigate selected links. As a metasearch tool, HotSheet relies on MetaCrawler, Yahoo, and HotBot. But the categories link to sites on culture, search tools, finance, travel, reference, government, health, games, software, and more.
A reference resource that functions like a "yellow pages" for finding a variety of businesses and organizations. AllPages.com is organized by subject and searchable by state and city.