I agree on Adsense - great earner.
Again, it depends on your target market... but here are a few more that convert very well for me:
(currently converting at 9.18%)
This program pays you $7/lead to give away a free (ebay) auction course & free toolkit. OR, you can set it up to earn a high commission (several hundred) on the sale (if people who take the free course decide to buy their backend offer).
by Fabio Marciano. The program is through ClickBank, but signing up at the link above will give you access to the links for all of Fabio's products. The actual OME site & landing page is:
www.theoneminuteebook.com
Pays out $74.99 per sale, 2 tier