AllAdvantage.com
This was the first service I signed up for. They pay you $0.50 per hour to surf and the banner isin't that big. You also get money for the hours your friends spend (if you refer them).
Desktop Horizon
This is another excellent service that will pau you even if you're not browsing the web. (You still have to be connected to the internet to view the ads)
mValue
This service is very similar to AllAdvantage. They pay you for browsing and the referral program is also the same.