It's worth noting that Duolingo is an example of a free web service without ads that generates a profit. In their case, they've crowdsourced the process of tran

It's worth noting that Duolingo is an example of a free web service without ads that generates a profit. In their case, they've crowdsourced the process of translating actual web pages while teaching people new languages. Depending on the nature of your site, perhaps you could take advantage of a similar crowdsourcing scenario?