one that immediately comes to mind is Constable's ace painting of stonehenge with a rainbow over it:
http://mrs.umn.edu/~deaneb/romantic/constable_stone.htm
but if you want something more modern art you could have a look at the megalithically inspired paintings at:
http://www.anne-madden.com/MaddenPages/paintings2.html
in my humble opinion (I'm currently floundering with an art project myself) pick some pictures you really like and concentrate on them - don't get bogged down by the enormous amount of stuff you'll suddenly realise is out there!
good luck
(got any mini cheddars??)