I have a Giro Mira,'carbon-effect' white which is great for visibility, very light, quite compact, comfortable, easily adjustable, one size fits all and best of all cost me less than £25.
In winter I often wear it with a light cap underneath - keeps out the draft thru' the vents, and you can use the peak of the cap to mask out the headlights of oncoming cars and avoid being dazzled.
I really think if some of the 'no-helmet' brigade actually tried a reasonable modern helmet they could be converted almost straight away.
I commute up to 23 miles (each way) and would not contemplate riding without mine, even though I have not had the misfortune of a commuting related accident. Some 30-odd years ago I took a dive over the handlebars and bounced 3 times on my head (no vehicles involved) and was lucky to get away with a lot of facial stitches. The outcome could have been much worse (I wasn't wearing a helmet in those days) and still vivid memories of that day are one of the reasons I would now always wear a helmet regardless of what anybody else chooses to do!