i always wear a helmet. even if i am just going down the road after a gear set up. i wear a piss pot style for trials and a traditional mtb one for xc. Vetta and Giro make some decent ones. your best bet is to go to your local GOOD bike shop and have a look. DON'T buy one from Halfords or Argos or anywhere like that, they don't really know what they are selling. but always wear one, you are asking for trouble if you don't.