GCF Learn Free.org offers over 750 free courses and over 200 free online classes for continuing education. Some of their courses may be useful to you, especially for your middle school or high school students (or for yourself!).
Why does GCF offer so much for free? For the same reason as Freely Educate, apparently! I was happy to read this on the GCF Learn Free site:
We believe there’s freedom in the ability to learn what you want, when you want, regardless of income or circumstances.
A place to start: View all of the free courses, organized by topic.
Free educational mobile apps! GCF has also created free mobile apps for learning Word, Excel, PowerPoint, Access, and Vocabulary. The apps are free and most are available for the Droid, iPhone and iPad: