This is something that sometimes actually crosses my mind. I acknowledge the existence of good people who rely on ad income (assuming they get something from ad views; I pretty much don't click on ads at all) and I'm willing to modify my behaviour to accomodate them. I sometimes unblock pages when they ask nicely (e.g. episodecalendar asks you if you could unblock ads when you have a free account, and since I actually get a real value out of this site (having my favourite shows pop up in Google Calendar, so I don't need to manually track new episodes), it was only fair that I unblock them).
From the division of Interesting Ideas That I Have No Time To Make, here's mine: an ad-block that instead of blocking ads, replaces them with crowd-sourced images of your choice - like "best of DeviantArt", Banksy pictures, ads for effective charities, etc. It was inspired by this picture I found once: http://editorial.designtaxi.com/news-banksycoke2405/big.jpg.
Another good option for replacing the ads would be to put appeals in place, things like the recent push for funding for the ebola hit areas in Africa, the appeals that followed tsunamis, famines, and other natural/humanitarian disasters, and so on.
Yes, that's also an excellent idea. The point is to allow people, per the quote I linked, to adapt the ad space to their own taste. Humanitarian appeals could be a good default. This could also solve the problem that some people complain about, that some pages have layouts built with ads in mind and become "uglier" when ads are blocked (not that I ever saw this actually happening).