This is a relatively new way of monetising your site. WidgetBucks have rich media ad widgets that display ads from various merchants. You earn money each time someone clicks on the ad widgets.
You can choose to have the widgets on your site displaying ads from certain product groups or you can choose the MerchSense option which runs ads that are relevant to your sites content and demographics. If you are wondering whether or not you can run WidgetBucks alongside Google Adsense and other ad systems the answer is yes. WidgetBucks can be run alongside all other ad systems.
Sign up is quick and easy and there is a $25 sign-up bonus which gets you half way to the payout minimum of $50. They also have an affiliate program where for a twelve month period you earn a 10% referral fee based on the commissions earned by the people you refer.
Give it a try and see how well it compares to other ad systems.