What Incentives Can You Offer to Forum Members for a Subscription Model?

Thread Title:
Converting Free Forum Users to Paid Subscribers
Thread Description:

WW Member lorenzinho2 asks about what a forum owner can offer to users as incentive for a paid subscription model. For high traffic, low CTR sites other options should certainly be explored, but what will make a member pony up the dough for a subscription. A few nice posts on what types of functionality, perks, and information might draw those wallets out of pockets.