D.M.
Some thoughts:
1) Avon ($10-$20 start up, not a MLM) and as big or small as you want to make it. I make about $26/month with Avon (LOL!) but I also get a good discount. If you want more info on that, message me. I don't want to SPAM you!
2) If you are into art or crafts, set up an etsy site. A few cents out of pocket and lots of possibilities!
3) If you write well, technical writing. The certification is not a requirement - you just need some contacts who need decent writers. Good writers are not easy to come by!
4) Examine your education & background. My "day job" is in the sciences and there are some people who work for me on call who come in, get data, go home, do the work, email me, etc. I have said this many times....someone who doesn't need to work full-time and doesn't need office space can be a COMMODITY in the current economy. SO look at your education and past experience and talk to anyone you know who is in your field to get ideas.
Good luck!