Google Adsense
Adsense has to be the number once choice when it comes to making money from your website. Millions of people are making money from the Adsense program, and as long as you have some kind of website then you can start to make money from it too. You can join the Adsense program for free, and when you log in to the website you will be able to choose the kind of adverts you want to display on your site - text adverts, banners, referral links, etc. You can blend these adverts in nicely to the content on your website, and then upload the code. You will start to make money every time a visitor clicks on your Adsense advertisements.
The amount of money you will earn from Adsense will depend on the content of your website (celebrity and picture websites wont earn you much whereas credit card and finance websites will) and it will also depend on the amount of clicks you get on your adverts.