Writing content is one of the biggest things you can do online. You can do paid forum posting, as previously mentioned, you can write blogs. I made over $4,000 last year doing that part time and it was quite enjoyable! Plus, the companies I worked for were very nice and sent out packages to me from time to time with all sorts of goodies. Sadly, the paid blogging industry is going downhill, but still something to look into.
If you are good at designing things you could become a graphic designer and work out of your home. I know of some people who do that around here and they are making some very nice money. Graphic design is not cheap.
