As much as I hate to suggest this kind of SA shit, some serious consideration should be given to stuff like donations to change people's avatars, add dumb titles to them, etc. and similarly, donations to change them back. And there should definitely be some way to encourage easy, simple microdonations of that kind.
Also, as much as I hate to suggest anything like this, look at Free Republic's history of horrible freepathons to raise money. I'm not suggesting getting THAT pathetic, but this is a site that has essentially existed on donations for decades. There are a number of sites that have existed for a long, long time entirely on user donations.
Another suggestion would be tiers of donations that give added schwag to the account, like visible bling (which you can choose not to display if you aren't a complete faggot or amplify if you are).