Schuberth C3 is very quiet, but I found the seatbelt style chin strap very uncomfortable, and the ventilation is poor meaning it's very very hot. Also, Schuberths have quite a deep bottom to the helmet which makes lifesavers a bit of a nuiscance sometimes as the helmet cathes your jacket.
I've now got the Shoei XR1100 which is quiet, although not quite as quiet as the C3, but has fantastic ventilation. I think you can get a mono coloured one for around the £300 mark. Alternatively look at the predecesor, the XR1000 as you can get them very cheap now.
Had both helmets neither were very quiet I'm afraid I guess it's down to what you ride and what protection you have
