Can I sell Snow Leopard DVD? Does the license transfer?
From the License Agreement page 2


  Transfer. You may not rent, lease, lend, sell, redistribute or sublicense the Apple Software.  Subject to the restrictions set forth below, you may, however, 
  make a one-time permanent transfer of all of your license rights to the Apple Software (in its original form as provided by Apple) to another party, provided that: 
  (a) the transfer must include all of the Apple Software, including all its component parts (excluding Apple Boot ROM code and ﬁrmware), original media, printed 
  materials and this License; (b) you do not retain any copies of the Apple Software, full or partial, including copies stored on a computer or other storage device; 
  and (c) the party receiving the Apple Software reads and agrees to accept the terms and conditions of this License.  


IANAL, but the terms of the licence clearly anticipated your wish to sell.