headset recommendations? (for my first fixie, for the street -- i'm looking for longevity here)

Most $25-$50 headsets have given me many years of service, regardless of brand.

I'm using a Cane Creek S2 and it's perfect. No complaints whatsoever.

so what exactly IS the benefit of getting the $100+ Chris King headset as opposed to the much cheaper Cane Creek headset?

well, a mechanic i know said he's used the same chris king on 3+ bikes and never had problems with it, but then, with a cane creek you can overhaul with new bearings many times before even approaching the price of the chris king...

You are buying a quality 100% made in the USA product which practices VERY sustainable environmental and production processes, while paying its workers a fair wage, and having the #1 quality headset. CK also promotes bicycling in Portland, OR. where they are based.
Did I say quality? I have heard stories of people who have one of the original headsets (20+ years old), and never chainging out the bearings, and still feeling as smooth as on day 1.
But all this comes at a cost.

Anyone know if there is any functional difference between the Chris King GripNut and 2Nut? Not that I really think I'll buy either.

if you want to dish out the dough, chris king makes the best headsets hands down, especially in terms of longevity.

the 2Nut allows installation of stack spacers and/or brake cable housing stops, the grip nut doesn't

also, if you have a steerer tube that's 1 or 2 mm too short for your head tube (with a normal threaded headset), the gripnut will make it work.