Without knowing the website it's difficult to say whether there's an Adsense alternative. A lot depends on the amount of traffic that you have. You can try kontera, adbrite and affiliate offers. Though you may be better off selling the website and developing a new site that it better suited to monetize with an adsense alternative. For example, a lot of micro niche sites only work well with adsense and it will be more trouble than it's worth to try monetize a site with a less favorable alternative like Adbrite.