Sourced

• Sanity is madness put to good uses; waking life is a dream controlled.
  • George Santayana, Interpretations of Poetry and Religion (1900)

• The criterion of mental health is not one of individual adjustment to a given social order, but a universal one, valid for all men, of giving a satisfactory answer to the problem of human existence.
  • Erich Fromm, The Sane Society (1955)

• Love, n. A temporary insanity curable by marriage...
  • Ambrose Bierce, The Devil's Dictionary

Attributed

• Of all the things I've lost, I miss my mind the most.
  • Mark Twain

• Sanity may take one of only two forms: either that of ignorance, or denial.
  • Derek R. Audette

• Sanity is a little box.
  • Charles Manson

Unattributed

• Sanity is for the weak.
  • Unknown, but appears as a quote from several Chaos faction units in Warhammer 40,000: Dawn of War

• Only the Insane have Strength enough to Prosper, Only those that Prosper can truly judge what is sane
  • Warhammer 40,000

• Who needs sanity?
  • Unknown

• Madness takes its toll. Please have exact change.
  • Unknown

• If you are keeping your head while others around you are losing theirs, perhaps you've misunderstood the whole situation.
  • Unknown (parody of Rudyard Kipling's If)