There are plenty of SEO affiliate programs in the ClickBank Marketplace under the e-Business and e-Marketing category. You'll find about 7 pages worth of SEO and SEO-related products to promote, with most of the commissions at 50 percent per sale. You could earn anything from $18 per sale up to $800.
There are even more options available when you go online, but the commissions are mid-range with various commission structures. There's also different kinds of programs: SEO plugins for CMS platforms like WordPress, link-building services, submission services, etc.
Since there's plenty to go through, take your time in choosing which ones to promote on your site. Think about what specific SEO services you'll recommend and whether they are the real deal. Get in touch with the affiliate managers and ask for a trial if possible. You can go into SEO forums or SEO blogs and check which ones are being recommended or talked about and which ones have a strong following.