Not all websites are well suited for Adsense. Some pages might be bigger earners with product placements from Amazon.com.
By filling out an application and submitting your website to Amazon, in much the same way that you became an Adsense publisher, you can become an Amazon Affiliate and begin listing the Amazon products of your choice on your website.
A particularly good example of a blog that makes good use of Amazon.com links is The Science of Salvation blog. This blogger makes his daily posts, and any books referenced in those posts he provides for sale through Amazon links, thereby offering his reader the best price from a reputable company, but also making himself a decent commission from Amazon on each completed sale.
A combination of Amazon affiliation and Google AdSense may be the way to go, or some percentage in between. This is something that you have to experiment with and find out what works best for your site.