Hot Weather Helmets - does anyone know of any?

[Alexlebrit]

I'm suddenly faced with a whole load of new gear to buy, having decided to do the trip in a buggy, and included in the list is a helmet.

Now I should point out the buggy has a four point harness to hold me in place, and the roll cage is "in theory" strong enough to protect me in the event of a roll, so really the helmet is all about keeping my head safe from things fly in - like mud, grit, stones, flies, small children etc.

I'd even been looking at downhill mountainbike helmets like

this Giro carbon fibre jobbie, which I'm sure would do the job, but are there any real helmets out there which would offer some ventilation and lightweight.

Thanks in advance (now wait for the wet weather clothing questions)