Ayrtek - light weight and good visibility. Funky design may put some off. I hzve not tried a new standard Ayrtek so I am basing my opinions on my old Ayrtek premier and Adidas Raw.
Masuri - arguably the market leader. Heavy in the hands but fine on your bonce. Very adjustable fit and looks alright (it grows on you). Optional extra of a stem guards, these offer good coverage and go unnoticed when attavhed, but some are put off by the price.
Gray Nicolls - possibly the best value for money compliant helmets. Also one of the most classic looking. I have not tried one on for size but the lack of ventilation would concern me. No neck guard or titanium grille option currently available from GN
Gunn & Moore - I beleive these are fairly cheap, looks classic and have a romovable grille. Again not one I have personally tried so cannot judge properly. Neck guards are also available I think.
Shrey - classic "Masuri look" and passes the new standards. I've not seen any in the flesh but read on here build quality was not always 100%. Very light and the additional nexk protector appears to be good value compared to some competitors.