title: Regex for alphanumeric, but at least one letter
body: <p>In my ASP.NET page, I have an input box that has to have the following validation on it:</p>
  <blockquote>
  <p>Must be alphanumeric, with at least <em>one</em> letter (i.e. can't be ALL
  numbers).</p>
  </blockquote>