Other (General Reference)
These resources, while not specifically philosophical, may be of use for general reference purposes.
Bartleby.com provides free online access to a wealth of literature and reference sources. These include such works as The Columbia Encyclopedia, The American Heritage College Dictionary, Bartlett's Quotations, and a host of poetry, non-fiction, and literature. All of these resources are available in full-text for free, but are generally older versions that are in the public domain, i.e., beyond the limits of copyright.
Librarian's Internet Index (LII)
The LII is a project by librarians in California to provide a Web directory of online resources across a wide range of topics. The LII is a good place to start when looking for a directory of reviewed and rated sites. The only drawback is that there is a bias towards all things Californian in the choice and selection of materials.
SearchEngineWatch.com has been around since the beginnings of the Internet. It provides ratings, tips, evaluations, and other tools to help Web users find and utilize the search engines most suited to their information needs. The site has a nice directory of specialized search engines (especially searching the "deep" and "invisible" Web), and is updated frequently. Most of the site is free, although there is a subscription section for those interested in learning more.