2011 June Solstice 2011-6-21 17:16 UTC.
http://aa.usno.navy.mil/data/docs/EarthSeasons.php

2011 Summer Solstice Doodle (First Day of Summer) is by Takashi Murakami.
http://www.guardian.co.uk/technology/2011/jun/21/takashi-murakami-google-doodle-solstice
http://static.guim.co.uk/sys-images/Guardian/Pix/commercial/2011/6/21/1308617449859/Summer-solstice-Google-do-007.jpg

"First Day of Summer, Doodle by Takashi Murakami, 2011."
http://www.google.com/search?q=Summer+Solstice&ct=murakami_summer-hp&oi=ddle
http://www.google.com/logos/2011/murakami_summer-hp.png

"First Day of Winter, Doodle by Takashi Murakami, 2011."
http://www.google.co.za/search?q=Winter+Solstice&ct=murakami_winter-hp&oi=ddle
http://www.google.com/logos/2011/murakami_winter-hp.png

The first hit of 1st search string mentioned:
http://en.wikipedia.org/wiki/Summer_solstice

And from 2nd search:
http://en.wikipedia.org/wiki/Winter_solstice

Yahoo.com noticed that from the summer side:

http://blazomania.com/2011/06/21/google-and-yahoo-doodle-on-summer-solstice-21-june-2011/