Some really great ones have been cited already but a glance 
at my syllabus for Introduction to Material Culture reveals 
my favorite. It is by Randall Jarrel, the poet. I discovered 
it cited in a New York Times Book review. It is from an 
unpublished manuscript:  I have used it a thousand
(hyperbole) times:


"Things last by being lost or broken

The shard is safest under the loess

The Ark sails under the waters of the earth"


of course there is always Green Day
"Time grabs you by the wrist, directs you where to go"

and the Bard of America Walt Whitman:


"The Past-the infinite greatnes of the Past! For what is the 
present after all but a growth out of the PAST"