For a single quarter basic introductory course, I recommend J. Matousek and J. Nesetril, <a href="http://books.google.com/books?id=I6wxfY2dUwQC">Invitation to Discrete Mathematics</a>, Oxford Univ Press, 1998.  I have taught from it several times - it is well written, clear, inexpensive, and fun on occasion.  It also has the advantage of being not overly ambitious in scope (compared to van Lint & Wilson, for example, excellent otherwise for a longer course and more advanced students), while still having a good selection of topics.