If you've got a hobby or interest, can create web pages, and are able to write articles, you can launch an affiliate program in your spare time.
If you've got a web site that you started as a hobby, think about using it start earning some income. In addition to writing content for your own web site, write articles for other web sites and insert a link that leads to your site in the author biography blurb. If you give these articles away as free content to other sites, the incoming links and the traffic you get will be worthwhile. Plus, the more links you have coming in to your site, the better your natural search engine ranking will be, thereby driving even more traffic to your site.