You will see the standard "construction" hard hat at most local races, and it was what I used for many years. The skateboarding helmets are what you will see at the bigger races, and what I switched to a couple years ago. I find the skateboarding helmets more comfortable, and less likely to fall off when leaning over a screaming nelson. I have had the construction helmets fall off leaning over, which is no good.

You will see all kinds, the cowboy hat is popular, as well as many of the US flags, eagles, etc...

Jim Allen has been wearing a different hat the past couple years. It looks like a ball cap, similar to the hats at this link. Looks like a neat route to go. To be honest, I don't think any of the hard hats we use would really do much good, but they do protect the head when trying to walk under some of those low ez-up shades.

http://abcsafetyglasses.com/mly-10033804.html