The legends of Stonehenge
The nice thing of doing research for a site, is that you always bumb into something you do not expect. Believe it or not: but I had no idea of any other legend surrounding Stonehenge, apart from the Arthurian one. Three legends I have found: "the Heel Stone", "Merlin and Stonehenge" and "Dancing Giants". If you happen to know more Stonehenge-legends, please let me know:

The Legend of the Heel Stone
The legend states that the devil was involved in the building of Stonehenge. He bought stones of an elderly woman from Ireland, and used his "magic" to transport them to their current spot on the Salisbury plain in England.
He then set them up. He got egotistical, and bet that no one in the nearby village would be smart enough to count all the stones. When asked, a local friar said "that is more than the canst tell", which means "that is more than can be told". That was the correct answer. Now the devil was mad, because his plan had failed. He picked up a stone, and threw it as hard as he could at the friar. The friar thought quick, and bounced it off of his heel. His heel was so hard that it caused a dent in the stone. To this day the stone is called the "Heel Stone", named by John Aubrey.

The Legend of Merlin
The legend of King Arthur provides another story of the construction of Stonehenge. It is told by the twelfth century writer, Geoffrey of Monmouth, in his History of the Kings of Britain that Merlin brought the stones to the Salisbury Plain from Ireland. Sometime in the fifth century, there had been a massacre of 300 British noblemen by the treacherous Saxon leader, Hengest. Geoffrey tells us that the high king, Aurelius Ambrosius, wanted to create a fitting memorial to the slain men. Merlin suggested an expedition to Ireland for the purpose of transplanting the Giant's Ring stone circle to Britain. According to Geoffrey of Monmouth, the stones of the Giant's Ring were originally brought from Africa to Ireland by giants (who else but giants could handle the job?).
The stones were located on "Mount Killaraus" and were used as a site for performing rituals and for healing. Led by King Uther and Merlin, the expedition arrived at the spot in Ireland. The Britons, none of whom were giants, apparently, were unsuccessful in their attempts to move the great stones. At this point, Merlin realized that only his magic arts would turn the trick. So, they were dismantled and shipped back to Britain where they were set up as they had been before, in a great circle, around the mass grave of the murdered noblemen. The story goes on telling that Aurelius, Uther and Arthur's successor, Constantine were also buried there in their time*.
(* Lacy, Norris J, ed., The Arthurian Encyclopedia, New York, Peter Bedrick Books, 1986, article by Geoffrey Ashe, p. 529.)

The Legend of the Dancing Giants
This legend states that giants living nearby, were dancing and circling around on the Salisbury plain. Suddenly and without reason, they were turned into stones. This legend was once popular because of the shape of the megaliths somewhat resembles the shape of giants holding hands.