You can try survey sites, like SurveySavvy.com, SurveySpot.com, and MySurvey.com. I've had some pretty good luck with those three - a few dollars once a week or so, but it doesn't take much time, so it's worth it to me.
Honestly, the biggest money-maker online for me is my blog. I write about personal finance, and I sell ads and use affiliate links to bring in some cash. I make about $100 a month with that, but it's taken me 2 years of writing to get to that point - it's definitely hard work!