GCF Learn Free.org Goodwill Community Foundation provides a site to learn for free consumer math, life, and computer skills. We've looked through the computer skills (Word, Excel, etc.) and found them thorough. (We've not looked through their life classes and suspicion they are secular adult in worldview and likely not appropriate for most homeschool children.) There are different options for the courses--you can either go through the self tutorial (which provides tests) or sign up for one of their online seminars taught by an instructor in the field.
Jan's Illustrated Computer Literacy 101. This site has free lessons on computer usage for basics, windows, word processing, data processing, web, and power point. Each area has an online course with lessons and tutorial.
K12Academics This site provides links to competitions ranging from debate, robotics, math, and spelling bees (including the famous Scripps). Not all competitions are open to homeschooled students.
Typing Pal Online. If you are looking for a free online typing program, here is one that is (or was at the time) really free and helpful.