Google AdSense

This is perhaps the most well known program for monetizing your website or blog. Registration is free, though there's no guarentee that you'll be accepted, so make sure that you have a quality website before you apply.They are very strict about their Terms of Service, so be sure to read them and stick to them - don't try to cheat the system, or you could get banned and loose all your money.I've been earning a steady income from AdSense over the last few months, and I would recommend it.