There a lot of ways how to earn from blog and that is what blogger does. They do a blog because they want to earn extra money.Blogging is just a hobby that in the other side can you benefit on it. There are a lot of site that offer that they will monitize your site and you can earn money on it and that is so wonderful. I had a few known and trusted sites that really pays you and they are legit blog monitizer.They are PPC or CPM site that pays every time someone visit your blog and click some ads.
GOOGLE ADSENSE - the most trusted PPC site in the web today and for the bloggers that pays everytime someone clicks the ads that is in your blog or website.
CHITIKA - also pays and uses target advertising for your traffic and visitors and that surely they will click the ads and you will earn on it.
BIDVERTISER - A trusted PPC site also that pay you every time someone click to the ads.
INFOLINKS - a in text advertising different from PPC but same if someone clicks the ads they surely pay you.
ADBRITE - A site thats offerd advertising space in your blog site and if a advertiser interested to your blog they will pay you and post their ads on your blog and someone also click on it they will pay also and in text advertising is also visible in your site,a full page ads also will see by your visitors and readers once they visist your site.
NUFFNANG - A blog community that only available in the Philippines,Singapore,Malaysia and Australia which if some advertiser interested to your site they will post the ads and someone clicks means money.