Zum Guldenen Stern: Bratwurste and, erm, Bratwurste... or saure Zipfel for variety. But it's in an old half-timbered house, which is canny.
Bratwurst Röslein: Despite the name, not just Bratwurst! Probably the widest menu of the traditional/central/touristy-but-not-too-much restaurants.
Barfüßer: Been here loads, mainly because I've never had a bad meal and only once had bad service. They brew their own beer on the premises too.
If you're only in Nuremberg for one meal, then make it Barfüßer and have the Schäufele & Kloß (or the Frankenschmaus, which is the same - pork shoulder and potato dumpling - but you get to try Bratwurst and Sauerkraut as well). But if you're around for longer, then I'd have at least one meal at Bratwurst Röslein (I quite like duck, but looking at the menu running up to Christmas, it's with orange sauce... but often I have the herring there, despite Nuremberg not being particularly sea-faring!)
Hope that helps.