Is there a built-in function or plugin to handle date formatting in JavaScript?

No, there is nothing built-in for Dateobjects, but there are a bunch of libraries to deal with and format them:

  • date.js
  • moment.js
  • XDate
  • Date and Date.Extras in Mootools
  • Date in Sugar
  • Dojo.date
  • a few functions in Mochikit
  • DateFormat (only PHP's date)
  • date at php.js
  • DataType in YUI, especially for i18n
  • date-functions.js, used especially by JQuery datetimepicker plugin

You've got some extraneous code that you can clean up:

var months = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"],
    today = new Date(),
    completeDate = today.getDate() + " " + months[today.getMonth()] + ", " + today.getFullYear();

$('#theEndDate').html(completeDate);

Using a library isn't always the answer, especially if you are only going to use it in one spot.