There are many ways to supplement your income by making money online and below I will list sites that are easy to use and will generate income from owning a website or blog.
Google Adsense and others like it, referred to as Direct Methods or PPC advertising are where you allow certain companies to place relevant ads on your site which generate money for you as visitors to your site click on those ads.
Yahoo! Publisher Network
Text Link Ads are also popular and can generate even more income and there are a variety of sites that offer such services. Sites that charge a fee, but that fee is taken from income they generate, so there is no out-of-pocket expense to you.
Text Link Ads
Once you start generating traffic to your site, mostly via search engines, then you can start adding code to CPM advertising sites, to which you get paid for impressions.
Another trend developing is the use of monetizing widgets you place on your site.
You will see many of these moneymaking methods placed on this site in the coming days, to show examples of how they work and what they look like.
There are many other ways to make money from a website, but these are methods to start you off.
Make sure to read the terms of service for each site and comply with them, most are very easy and common sense rules.
Good luck and make a lot of money!