Google Scholar:  a subset of the Google search engine that searches primarily journal, book and document files.

RefDesk.com:  a HUGE amount of information at your fingertips. A good place to check facts, find calendars, converters, almanacs, current news stories, etc.

InfoMine:  scholarly Internet resource collections, by subject or by keyword search. Highly recommended.

Librarians Indext to the Internet:  links to websites, arranged by subject,  that are generally considered to be reliable and accurate. These sites are pre-screened by professional librarians to exclude biased and commercial sites.

The Merck Manuals Online Medical Library:  a series of online healthcare books for the medical professional.

Dorland's Medical Dictionary:  online version of the classic resource.