Stonehenge is such an obvious subject for LEGO that it's been done many times. Here are a few of my favorites:
Tony Sava - note that he took pains to be very accurate here
Etzel87, this time in micro
Alex - I just loved this one
Koffiemoc - another micro version
Orangyal007 - This one made me smile. I think those are Quatro blocks, Duplo's even bigger brother.
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In the beginning there was the stone
These giant LEGO blocks weren't really supposed to depict Stonehenge, but that was NeeS's impression when arriving at Legoland Germany. I have to agree.
There are other LEGO versions of Stonehenge out there, but they do start looking similar after a while. Can you believe I got through this whole post without one mention of Spinal Tap? Oops, there I did it.