Some affiliate programs keep paying you every month after someone signs up through your link.
Which are the best paying? How much do they pay?
Which ones are easiest to get people to sign up for?
Imho, the "best" affiliate program is probably adsense + a site that people like to come back to. An affiliate program is only useful, valuable, in as much as you have people coming to your site.
There are some programs in the dating space that will pay you monthly every month people stay members of the site, as well as gambling / casino related programs. However, with gambling in particular, you'll want to check your local laws, etc, before pursuing them.
I disagree there. Adsense is probably one of the worst paying, and it's not residual: you don't get paid month after month from a single user action. That means to retain your income you have to have the same number of users returning and clicking the ads every month. I was referring to programs like the dating ones you mention, other membership sites, hosting, etc., and which are the best of them.