Advertising
Amazon Associates: This easy-to-use system allows you to place ads on your page and earn a commission from anything purchased through the link on your page. It can be used for websites and blogs, and is a great tool for making extra money from your site. It also has a very easy-to-use interface that allows users to pick which type of advertisements they would like displayed.
Google AdSense: The most familiar to most small business owners, this program allows you to customize your ad for your individual page and pays you per click. Watch the informative video from Google for more information and learn about ad placement and optimization.
Google Adwords: Adwords is a service offered by Google that lets users bid to have their ad listed beside keyword searches. It is a very targeted approach to marketing and users only pay when their ads are clicked on.
Other Affiliate Programs
An affiliate program is a when an advertiser pays a website owner to purchase advertising space on their page. Amazon Associates and Google AdSense are the major affiliate marketing programs online but there are thousands offering every type of product. It is best to choose an advertiser that is not a competitor but a compliment to your product or service. For a list of over 22,000 affiliates visit Affiliate Scout.
Which ads are working? If you want to optimize your ads, the best website to use is 
OpenX. It allows you to monitor yours ads and will report which ones are working and
how many people are clicking on them.