The Collaborative International Dictionary of English v.0.48:

Speller \Spell"er\, n.
   1. One who spells.
      [1913 Webster]

   2. A spelling book. [U. S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

speller
    n 1: someone who spells words [syn: speller, good speller,
         poor speller]
    2: an introductory textbook to teach spelling