Adbrite and Adsense are the two advertisement programs that I have used the most but there are many others that have gotten great feedback and can be used to generate income for all types of blogs.
AVN Ads (adult ads): http://www.avnads.com
Black Label Ads (adult ads): http://www.blacklabelads.com
Crisp Ads: http://www.crispads.com
Miva MC: http://www.miva.com/us/content/partners/arx.asp
Revenue Pilot: http://www.revenuepilot.com
Text Ad Links: http://www.text-link-ads.com
Yahoo! Publisher Network: http://publisher.yahoo.com
Value Click: http://www.valueclickmedia.com/Publishers.shtml
The majority of these ad programs can be used together. Many blog owners use multiple ad revenue programs on their blogs in order to get more revenue from a wider variety of sources. While I primarily use Adbrite I have also used the Yahoo Publisher Network and Kanoodle to sell ad space and buy some. Some of these programs will pay you per impression which means you earn money regardless of whether a reader clicks an ad.