For the wheat I brewed today, I used some NZ Hallertau with a 8.7% AA. Very nice for bittering. Used some lower AA German Hallertau for a bit of aroma.
I have used some Saaz with a 7.7% AA rating, it's good stuff, too.
By definition noble hops are the traditional flavor & aroma hops that are low alpha. Those would be the German/European hops like Hallertau, Tettnager, Saaz, Spalt, etc and the British nobles like Fuggles and Goldings. Higher alpha hops like German Magnum and British Challenger are grown in the same areas and do blend well with their noble companions but they would not be considered noble hops themselves.
As BigEd pointed out, European noble hops are normally low alpha. I think the higher alpha "noble" hops that are available are usually domestically grown. Have some 6.5 AA Saaz that worked well in a pilsner. I think it was the 1.5 ounces of homegrown Saaz at flameout that really brought it home though.