However, the information provided by Wikipedia needs to be taken with a grain of salt. Entries may be inaccurate, biased or both. Information should be verified another source.

I would agree with Oron - there are no good substitutes to Wikipedia, which is the greatest database of human knowledge ever created. Wikipedia itself would be best classified as "general knowledge" or information that is less specialized than information published in, say, a scientific journal. If the information in Wikipedia is insufficient, you will need to access a specialized source of information. I would suggest using Google Scholar as a starting point, which will locate journal, periodical and other highly specialized sources:http://scholar.google.com/

I can't think of anything comparable to Wikipedia but there are two great knowledge engines: Wolfram Alpha https://www.wolframalpha.com/and evi http://www.evi.com/ (formerly TrueKnowledge).They both take questions in natural language and attempt to answer them using information collected from the internet, so they are great for getting factual answers.