Popup, interstitial and expanding ads are pretty annoying since they interrupt the flow of the site. But other than that, I think more ads is the way to go - servers don't run on good intentions and we're all grateful for the free community we have here. Ad-free paid memberships or removing ads for donors might also work You may also want to look at some affiliate opportunities if you can find products that would be valuable to the community - affiliate revenue would likely outperform CPC or CPM rates. And maybe sponsored advertorials for advertisers who would like to reach your audience directly with long-form appeals and special offers. Point being, I think there are plenty of ways to offer ads that also have some value for the community and therefore don't feel "spammy."