A whole bunch of tongue-in-cheek "Is $xyz down?" type sites. Simple footer ad, maybe an affiliate link or two for a competitor and also my web hosting provider,

A whole bunch of tongue-in-cheek "Is $xyz down?" type sites. Simple footer ad, maybe an affiliate link or two for a competitor and also my web hosting provider, some sort of social media affiliation like a pre-canned tweet with a complaint in it - they all pay for their domain name and hosting, some turn $100+ monthly in ad and affiliate revenue as well. I'd estimate about $450ish on a good month, but it has taken a while to get to this point. I've stopped actively promoting any of them now, but the most profitable ones I'd probably invested 30-40 hours each in promoting.