Productivity hub Lifehacker recently posted about Stanford Engineering Everywhere, which offers free, full engineering courses online. They've also posted a pretty extensive list of free online college courses in a variety of subjects.
This is a great way to challenge advanced students, expose all of your students to college-level work and materials, and give them a taste of what they'll be expected to do with all this stuff you're teaching them.
I haven't explored everything yet, but I'm sure I'd find some lesson ideas and resources I could use in the classroom as well. Of course, you can also use these courses for your own benefit, be it a thirst for knowledge or indulging in nostalgia for your alma mater. If you're considering graduate school, this could help you with the vetting process for schools and areas of study. If you find anything particularly interesting or useful, please post a comment or email me.