DragonByte User Upgrade Coupons is a powerful tool for incentivising people to sign up for user upgrades.
Coupons can be limited to individual user upgrades, and even be given different values for different user upgrades. Fully supports recurring subscriptions, allowing users to be "grandfathered" into their existing coupons for as long as their subscription lasts.
User Upgrades are a great way to monetise your site, and with User Upgrade Coupons from DragonByte, they are taken to the next level. You can optionally add temporary user group changes on new user creation (even supports manually created users via the AdminCP!) that expire after a set period, as well as create powerful coupons that let you fine-tune the price of your user upgrades.