I think you have to make a choice between a well-vented "racier" helmet and a poorly vented "commuter" style. No helmet is going to vent without having some holes in it.
Visit bike shops. Try some on and find out what fits - people's heads are shaped differently, and some brands fit some people better than others. You'll be able to find something you like.
Also, be aware that you can get plenty hurt at 25 mph. The time my helmet saved my life I was going 21 before I crashed. Unlike motorcycles, it seems like the weight distribution of rider and bicycle has a tendency to throw the rider violently on your head. You don't have to be going super fast to benefit from a helmet.
Last edited by OakLeaf; 08-09-2011 at 10:11 AM.
Speed comes from what you put behind you. - Judi Ketteler