SEOPress does have an affiliate Program. You can get paid to send referrals to SEOPress through your special link. Here are the details on how to become an SEOPress Affiliate.
Long Tail Pro has an affiliate program with the Share A Sale Network that includes a two-tier (sub-affiliate) link as well. Promote Long Tail Pro and earn through their affiliate program.
All In One SEO is a Wordpress Plugin made by Semper Plugins. The All In One SEO Affiliate Program is part of the Share A Sale Network.