Today is the first day of Summer, also known as Summer Solstice which happens today, June 21st. Some of the search engines have logos for the day, but Google has 4 different logos for the day.
If you go to Google.com and click on the logo, it shows you a new logo, 4 times, until you end up on a search result for [summer solstice]. Here are the four Google Doodles for Summer in order:
Yahoo has two logos, one animated and one static:
Search Engine Roundtable:
And on Google Germany Google has a logo for Jean-Paul Sartre's 105th birthday. Jean-Paul Sartre is a famous atheist writer, playwright with many well known books and plays. Here is his Doodle:
It is also the first day of Winter in other locations, such as listed on Google Argentina and they have 4 logos: