Mountain-biking helmets really are different from road helmets.
Mountain helmets typically have more venting at the top of the helmet, so warm air can escape when you鈥檙e grinding up a long slope in the big ring. So take a look at the Bell ($90). It鈥檚 an excellent all-around mountain helmet, with plenty of ventilation and a removable visor.
THE ALTERNATE: Here鈥檚 a new take on the trad MTB helmet: The POC ($160). The Trabec inherits features from POC鈥檚 ski helmets, such as a more all-head fit than some other helmets, which tend to sit on top of the skull. Plus it鈥檚 a very cool-looking helmet.
For something more urban, check out this this next helmet.