A "Link Award" is an absolute must-have. Members may not think to link to your forum on their own, but they will if you give them a pretty graphic for it. Just be sure to tell them not to spam or place the link where other forum owners might disapprove; that would make you look bad.
If you really want to see the Link Award theory in action, you could also offer awards for linking to your other sites. (Especially if the topic is related.) Not only will this give you a little more publicity for them, but as I said some members will do anything to get lots of awards.
