• Declare CS as soon as they are able (after grades are in for CS302) and watch email for CS job and internship opportunities as the Department is contacted and informs undergrads and graduate students about them.  http://pages.cs.wisc.edu
• Try the ACM (Associated Computing Machinery) contests and other programming and design contests that the Computer Science department sponsors teams.
• Check out the UPL (Undergraduate Projects Lab)
• Try using Processing (Lab 12) to create an animation using fractals. 
  Here is a very impressive and creative animation: http://youtu.be/mPYeTJd8klQ
• Solve some of the programming problems on http://projecteuler.net
• Solve some of the programming problems on http://codinggame.com
• Download some Java code and program your own robot to win battles against other robots. http://robocode.sourceforge.net/
  

Finally, they can always learn a new language (like Python) on their own.  Python is useful for many things and there is a Python tutorial behind the "Java Visualizer" page.   Click Java Visualizer and then remove the "java_visualize" part of the address, to get to a Python tutorial.  Now, that they know how to program, they can learn many new languages and program structure patterns.