Residual income means you work once and keep getting payments multiple times for the same work. There are many types of residual income
1. Royalties from writing, performances etc.,
Negative: This type needs creativity and skills to create the first time.
2. Some sites pay repeat commission for referring customers. For example Amazon keeps paying you whenever the customer shops.
Negative: But this needs internet marketing skills to make the customer to shop through you first before anyone else.
3.Second tier commissions from websites are another source of residual income. If you refer some one to a website and that person becomes an affiliate then you can get a portion of commission from their earnings.
Positive: a. As in many cases, it is only a free sign up, this is an easier task requiring lesser internet marketing skills.
b. Simultaneously you can try to market directly also to earn income.
Here are a few sites where you can earn residual income of the third type
This cost per action site pays you money for giving away surveys/ downloads, etc., Basically, you get a valuable content (good PLRs available)and lock it behind the survey. The visitor takes the survey first. Then they will get the content. You get paid for each survey completed.
This cost per action site has an other trick also. You get 5% of what your referral earns. That is a neat trick is it not.