i have been looking for a plugin developer that could make me a plugin that gives user special ability when they donate. For example like a cool name tag that stands out from the rest, and customized enchant that are unlike the enchantments on mc. pleases let me know if anyone is interested ill be happy with working with you.
On-topic: There are plugins to edit a person's nametag and others for special abilities/enchants. You could combine those with a donation plugin (Buycraft / Donationcraft) to get what you are looking for.
I'd love to help you as much as I can... I am a really talented coder although I do not like to publicly release my work I will be glad to code with/for you, and I would like to make this plugin seems like a "challenge" or a "Fun project"