I like <a target=_blank 
href="http://library.artstor.org/library/ExternalIV.jsp?objectId=8DtZYyMmJloyLyw7fzpxSXkp">Claude 
Lorrain's <i>View of Tivoli at Sunset</i></a>.  This was in the <a 
target=_blank 
href="http://www.nga.gov/exhibitions/lorraininfo.shtm">special exhibit 
on Claude Lorrain</a>, which is why I didn't get to photograph it.