This year has a lot of good candidates, but I'll also have to go with Sierra II, as he went from seasonal to the middle games of Dania, and came away with a wins title. Honorable mentions:
Diego (now close to the "king" for top frontman at Dania)
Medrano (from a surefire leave out to top early gamer)
Tommy (from "why is he back there" to a wins title at Orlando)
Alliez (I never thought he would be a late gamer, but he's really taken off in '08)
Arrasate (Rightfully in late games at Miami now)
Ricky (possibly the best back at Miami after the 'big 2')
Alejandro (looks comfortable in back now)