DuckDuckGo
A general Internet search engine, but unlike Google and other general search engines, DuckDuckGo does not track your usage. If privacy is important to you, you should consider switching to DuckDuckGo.
Google Scholar
A Google search interface that attempts to limit results to scholarly sources. Useful for finding that elusive article to which you don’t have access.
TinEye
A reverse image look-up tool. If you need to locate the Internet source for an image, upload an image file and TinEye will attempt to resolve an address for you.
WolframAlpha
An Internet calculator providing answers to mathematical formulas, unit conversions, physics and chemical computations and more. Want to know how many days it’s been since February 1, 2002? Enter “How many days has it been since February 1, 2002?”