Oli - not sure of your price range etc but whenever I buy new sunglasses I will be getting a pair of Cutler and Gross. I know the model and colour already but have a perfectly good pair of Persols so cannot justify them at the moment.
thebrownman swears by their quality, which seemed excellent to my layman's eye and the styles are great.
I know they are on the more expensive side but "buy once, cry once".
With glasses it is about trying on a many pairs as you can....