If you want to promote casinos without getting payment from casinos (I don't count referrals as payment here), then it's best to promote the most trusted ones. For instance, you could try Fortunejack, Bitcasino.io, Sportsnet.io, Bustabit, Primedice. I think it's good if you choose this approach, because many similar website choose another one and probably get paid by no-name casinos which then appear as 'the best casinos" on the website that does the promotion.