If you need some quick information about a topic you know nothing about check out encyclopedias, dictionaries, and almanacs for that discipline. Browsing through these sorts of reference materials can also be a rich resource for new ideas.
Should you use Wikipedia as a research tool? Yes. The general rule of thumb is to use Wikipedia as starting place, but not as a cited reference. This is the case for any encyclopedia. They are wonderful for introducing you to a topic, but should not be used as a source in bibliographies or works cited lists.
For general reference check out refdesk.com: "Since 1995, Refdesk is a free and family-friendly web site that indexes and reviews quality, credible, and current web-based resources."
Wolfram|Alpha can answer any math problem you give it. It also works well with answering natural language math questions (I.e. what is twelve divided by six rather than 12/6.)