How to monetize a message board?

A few days ago I sold one of my domains for a pretty good price and it made me think about what I should do with my some other online properties, that run publicly under my name. One of these sites is a board with about 9000 members hosted on a pretty good domain. It's kind of a hobby of me and I definitely don't want to get rid of the board, but growing the site is very difficult, takes time and/or is expensive.

The board also doesn't make much money unless I use layer ads and bother the users/members, which is something I don't want to do. Any other ideas how to monetize the board in an ethical way? Curreently it's only Adsense and Amazon, but maybe there is another solution that I could use? Does anybody have an unusual experience with monetizing a board?