These are some decent alternatives to Wikipedia, the online wiki that anyone can edit and contribute to, other online encyclopedias have taken a more restrictive approach as to who can create an article, some of them will ask the author to use his/her real name as well as proving accreditation of any qualification the author claims to have, others do not allow users to contribute articles and are written by experts hired by the company, the final goal is always the same, to create a reliable accurate encyclopaedia containing a wide range of subjects for students, researchers and those in search of knowledge.
Citizendium: An encyclopaedia organized like a wiki, it asks people to verify their credentials before they are allowed to edit pages, people editing Citizendium pages have to use their real names, it has less content than Wikipedia but there is little vandalism and information tends to be more methodical.
Scholarpedia: This free online wiki encyclopaedia only accepts as authors verified experts in the field, their articles are then peer reviewed and any posterior change to the article needs approval from its curator, normally the original author.
iDebate: A discussion site of pro and con arguments and quotes, a place for people to debate about worldwide issues using legitimate supporting evidence derived from reliable sources.
Britannica: Premium online encyclopaedia, in the free version you can only read small article extracts and follow links to external sources related to the researched theme, it should work well for low level queries or to be used as a dictionary but for extended research you will need to upgrade.
Questia: Free encyclopaedia with articles from the Columbia Encyclopaedia. Only a small part of the articles are free you get bugged to upgrade for premium access to access profound information using Questia’s broad collection of online academic journals and articles.
Encyclopedia.com: To elaborate the articles this free online encyclopaedia uses a mix of over 100 trusted sources like dictionaries, facts, word origins, biographies, synonyms, etc. An excellent research tool with a wide range of subjects that will be of great use to students and people investigating a particular subject.
Encyclopedia Smithsonian: Online encyclopaedia from the Smithsonian Institution, a US research institute and museum, their free educative encyclopaedia includes articles with links to their exhibitions, in some cases complemented with audio and video.