I've tried a lot of helmets both in personal and professional climbing environments and it took me a long time to settle on which to buy. I was very tempted by the 'weightlessness' of new style EPS helmets, however being "one-hit wonders", I felt the durability and longevity of this helmet won over weight, for me personally. Perhaps on longer expeditions where weight is key I will decide otherwise! But for its current use, in both personal climbing, and while instructing groups, this classic helmet fits the bill.
The helmet is easily adjustable and comfortable. I have found it keeps my head near completely dry on wet days, but also offers discreet venting for hot days.
I nearly bought the pony-tail friendly Petzl, and while that is both a pretty and practical helmet for women, I can fit my pony-tail neatly between the back of the helmet and the adjustment strap.
The Black Diamond Half Dome is available from many good outdoor retailers - both online and on the high street. CE and UIAA-certified.