Although this one is the most favourite in my list bit I put this in #4 because not as easy as other 3 above and it takes time to make money from Google AdSense.
You need a website (which anyone can create now a days) and some tricks to bring the traffic on your website so that can earn money from AdSende and other Ad network.
We AdSense prepared one of the best course on AdSense earning which thous and of pepole in India and all over the world have used and now they are earning $200 to $1000+ per month.
