The National Security Agency better known as the NSA has resources for students interested in codes and ciphers. If you have students interested in codes and ciphers (and a lot of students who like programming seem to also like those things) than this may be of interest to them. There are puzzles, games, and lots of information there. Who knows you may even find some ideas for programming assignments or supplemental information for projects you already use.
There is also information about summer programs for high school and college students. Let your students know that there are oppertunities for puzzle solvers out there.