Ads are acceptable though it may slow down site growth. If the ads don't get in the way of your users, they won't mind as much. Also, a donation button might be worthwhile as well; but don't expect it to make much money for you. Consider for example the sob story at the top of the page: http://gnosis.cx/TPiP/. Two donations out of 1,000 book downloads a month.
If you can add some extra/useful features to the site, why not setup a premium subscription? Set the price low to start and that will likely get more revenue this way.
Comments
Ads are acceptable though it may slow down site growth. If the ads don't get in the way of your users, they won't mind as much. Also, a donation button might be worthwhile as well; but don't expect it to make much money for you. Consider for example the sob story at the top of the page: http://gnosis.cx/TPiP/. Two donations out of 1,000 book downloads a month.
If you can add some extra/useful features to the site, why not setup a premium subscription? Set the price low to start and that will likely get more revenue this way.
Good luck!