Quotations (as collected by Paul Chernoff)

Direct link: http://math.berkeley.edu/~chernoff/quotations.html

The very last one is from a poem by Antonio Machado (scroll at the very bottom of the front page of my blog to see it).

And here is the one above it:

A good mathematical joke is better, and better mathematics,
than a dozen mediocre papers. -- J.E. Littlewood