Thats a toughie,, more personal preference,, I have the HJC AC-X1 and like it,, I'd like the CF version of this and I'd like to see the Hebo CF helmet,, heard it was way light!
theres a newish Airoh helmet. weighs about a kilo, or 3 pounds. but its not cheap, not in NZ at least. but it gets good reviews and its airoh so im sure its good quality
Whatever kind/ brand you get, you'll probably want one that is "Snell" rated. There also is a European standard ECE 2205, I'm not sure if that number is correct. The snell helmets are tested to a higher standard than DOT helmet. The Snell foundation updates their standards every five years so a helmet with a 2005 sticker may be only a few months old or it could be 4 1/2 years old. I have an HJC, Snell rated, that has been good for me, I might get a Bell next time around.