This page in a nutshell: This page overviews the history of the Wikipedia logo, from the original US flag example to the current puzzle sphere logo. Originally written in 2003 by Jrincayc and Eloquence.
The Wikimedia Community Logo was created in 2006 by user:WarX as a public-domain logo intended to be free of trademark and visual identity guidelines, that community members and groups could use and remix as they wished. In 2008 it was chosen as the new logo for Meta-Wiki, replacing the Wikimedia movement logo, with "Wikimedia Meta-Wiki" underneath.
The second place logo (International logo contest/Results) by Neolux was appointed as the logo for Wikimedia by logo contest organizer Erik Möller on October 15. A version was adopted by Neolux for the Wikimedia Foundation on October 15, 2003.
2006-2012
Introduced in January 2006 based on modifications made by Wikimedia Foundation.
2012-2016
Introduced in March 2012 based on modifications made by Wikimedia Foundation.
2016-Present
Introduced in July 2016 based on modifications made by Wikimedia Foundation.
The second place logos (International logo contest/Results) by Neolux was appointed as the logo for Wikimedia by logo contest organizer Erik Möller on October 15, 2003.
In the early days of Wikipedia, founder Jimbo Wales uploaded an American flag as an example logo. Needless to say, it was never intended to be the permanent logo. See the following discussion at OldWikiPediaLogo.
Nupedia logo
2001
The Nupedia logo was originally sent to a Nupedia logo competition by Bjørn Smestad, and was used by Wikipedia until the end of 2001. It continued to be used after this time on special pages such as search results.
This "silver ball" was created after the International logo contest/Ratification as an improvement of the Paullusmangus logo. The English Wikipedia switched to this on Oct 12, 2003 after it achieved a general consensus of 21 preferring it, with only 3 preferring the previous logo (vote page on Oct 12).
A new, internationalized variant was later uploaded without much discussion, as the previous logo was not available in internationalized form and the differences were considered minor. See #2003 international logo contest for more details.
Wikipedia logo v2
2010-Present
In May 2010, the revamp of Wikipedia puzzle globe started in 2008 was completed, and new logo has been implemented along with the new Vector interface.
Due to strong feelings by some Wikipedians who considered this logo inferior to the old one, the designer, User:Paullusmagnus, put this picture on his user page in a bit of self-deprecating humor:
French Wikipedia logo, 2002-03French localised logo implemented on June 2002 under French community fork threats, with some controversy. (The moment when some French community members took interest in international matters.) The French Wikipedia began to use the same logo as other languages in October 2003.
The "silver ball" was created after the International logo contest/Ratification as an improvement of the Paullusmangus logo. The English Wikipedia switched to this on Oct 12, 2003 after it achieved a general consensus of 21 preferring it, with only 3 preferring the previous logo (vote page on Oct 12).
By Oct 17, after it was implemented, the vote had changed to 23 supporting and 12 opposing (vote page on Oct 17). Arguably, the result is still somewhat biased– the people who were strongly opposed to the winning logo were highly involved in the final optimization process, while the people who were strongly opposed to the new variant quickly headed to Meta to vote it down as soon as it went public. In any case, there appears to have been wide support for the new variant.
There was some controversy (See Logo feedback and Talk:Logo feedback) over switching the English Wikipedia to this logo due to several reasons.
The first was lack of publicity for the poll over this, despite being linked to from many Main Pages, the mailing list, and w:Wikipedia:Announcements (the announcements page asked for comments on Oct 1 and votes were requested on Oct 13).
The comment page quickly formalized in a "Better than original logo / About the same / Worse" poll, which was conducted fairly informally.
The decision to modify the logo was made during the logo ratification process.
Some people were strongly opposed to the winning Pallusmangus logo and decided that the logo should be modified.
The number of people participating in the logo variant process was probably around 20 or so (at least until the logo was switched at which point it increased to around 40) compared to the 188 valid ballots in the orginal logo contest.
After a few days on the Main Page, User:Nohat uploaded a new, internationalized variant. The logo in use was quickly replaced with that variant without much discussion, as the previous logo was not available in internationalized form and the differences were considered minor. This is the logo that is now in use (in different translations) on most Wikipedias.