He has a limited character, but I like Umaga.
Bring him back S-T-R-O-N-G with a manager by his side(***)... Crush Funaki, Jesse and any other 'disposable' faces, slightly harder fought victories over maybe Matt Hardy, Finlay, Truth and the like and then, the one many want to see, a fued him with Taker.
(***OR.... As previously suggested above, give him a handler a la Kamala/Kimchee. Explain that since he has been away he has become more in touch with the savage side of his being and that he can no longer be left to roam free around the WWE. This would still require a manager to give the moster and his handler direction/instruction within the storyline, but I like the idea of a mystery managerial entity being behind Umaga and the handler being deployed to destroy Taker... A bit like when Whipleman sent all his monsters after Taker around 93/94 but cloaked in secrecy... Plus you have a good ol' fashioned "who is it?" storyline to revolve around whoever you like when it's time to reveal who's been pulling the strings - Whether it be Edge, maybe a heel HHH or something fresher still).
Once Taker's eventually done with him have him trickle back down the card and have him fued with Kennedy whilst clashing with any face champs in the interim (and if he's still about when guys like Ken, MVP, Jeff & co. have cemented their perceived future ME spots then you have a good monster to throw at them when needed).
Realistically though, the only gold I see in his future would be ECW.