adsense

rent advertising space (with a popular website)

affiliate marketing

article writing, blogging, etc.

digital products, domains, etc

virtual services

trading shares, trading currency

What else is there?
Don’t include ways like survey filling out or anything that doesn’t have the potential to make at least $200/month.

And nothing illegal.
And “check out this blog” is not a way of making money online.
I don’t want links.