Why dont you add a rank for people who donate to the site (if you can add a paid subscription or something) that way they can be noticed for donating towards the site and have a cool new badge
I don't think ientry really need donations.
Okay, here is an idea: give a rank for those who have their own forum sites. Call them Forum Lovers or something like that.
Thats pretty much just advertising more. You have a signature where you can advertise.