Not all sites that look like Google are Google. Though there are some official humor-powered Google sites (like Google Klingon, Elmer Fudd Google, or "Google Pigeon Rank"), the following screens are all unofficial:

Aloogle searches all things Weird Al Yankovic

Aloogle searches all things Weird Al Yankovic.

Koogle is the kosher search ; a Jewish search engine

Koogle is "the kosher search"… a "Jewish" search engine.

Elgoog is Google... backwards

Elgoog is Google... backwards (today, with a turkey for Thanksgiving).

Gizoogle is a gangsta rap flavored Google

Fo' shizzle my nizzle... Gizoogle is a gangsta-rap flavored Google.

Toogle is a mix between Google parody and ASCII art creator

Toogle is a mix between Google parody and ASCII-art creator... enter any search term and a related image will show drawn with letters only.

Booble is censored here

Booble is censored here. This search engine had the honor of getting contacted by Google's Senior Trademark Lawyer, and was later on renamed to "Bible."

Spam Google finds nothing but spam

Spam Google finds nothing but spam. It's just like Google, without good results.

The Google FBI and CIA search

The Google FBI & CIA search. (By Semmelbroesel.)

Google April Fool's search

Google April Fool's search was released on April 1st, 2004 as seemingly official Google search – it searches only pages related to April Fool's.

Cthuugle, the complete HP Lovecraft Search Engine

Cthuugle, the complete HP Lovecraft Search Engine.

You can search 0 web pages with Google Zen

You can search 0 web pages with Google Zen. You might prefer hitting the "I'm feeling" button... (By XlBrooklyn.)

Ghoul searches for brains only

"Ghoul" searches for brains only...

Google circa 1960

Google circa 1960. "Please print query clearly... mail to Google Search Request... and allow four to six weeks for results" (By Google employee Kevin Fox.)

UnderGoos is a search engine for underwear

UnderGoos is a search engine for underwear.

Note: You can find the search engines shown here by searching for their title in Google – Aloogle, Koogle and so on (this is their "Googlonym," or "Memomark"… a bookmark that is a Google search). Sometimes, only a mock-up exists, and not a full-fledged search engine.