Buying a helmet is at least as complicated as buying your first bike. Probably because the choices are so vast. And the consequences so great. The proper helmet can save your life. And your brain.
Helmets come in all shapes and sizes. Half helmets cover only the brain itself. There is no protection for ears, face or chin. There is no doubt that there are many cool looking helmets of this design. And as long as you never need a helmet, they are great. But there are no SNELL approved half helmets. Buyer beware.
Three quarter helmets add protection for the ears and side of the face. They have no chin protection. They usually have visors that flip up and/or are detachable. They are a significant step up in safety from the half helmets.
The most protection is offered by the full face helmets. They offer full face protection, including the chin. On some versions only the visor can flip up. On other versions the chin area and visor flip up. Beware of the chin flip up versions. There is concern that the latches that allow the chin area to flip up may activate during a crash, obviating the safety traits one is seeking with a full face helmet.
I highly recommend you buy your helmet from a local retailer. Not all helmets fit all heads. Thus, going to a store and trying on a helmet is usually the best approach. It seems only fair that if you use a retailer to help fit you in a helmet, that you buy from that retailer. If no one buys from retailers, there will be no convenient way to try on gear before you buy.
I own a Arai Quantum II. I considered the high end Shoei's and the Arai's. I wanted a Snell approved helmet. Snell is a private foundation, and a helmet must pass their rigorous tests to get the Snell approval. This testing is much tougher than the minimum standards required for DOT certification.
A nice feature of the Shoei's and the Arai's is their light weight compared to some of the other helmets I tried on. I like both lines, but the Quantum II just plain fit better. And fit is everything, once you have narrowed your search to Snell approved helmets.
I purchased my helmet from Cycle Gear, 10998 North Freeway, in Houston, Texas. I was very impressed with their store and the knowledge of the sales help. Buying a helmet isn't a fast process. For one thing, you should wear your potential purchase for fifteen minutes or so to make sure it will be comfortable. The guys at Cycle Gear had no problem with the 30-45 minutes I took to make sure of my choice. They had a great selection of helmets. I highly recommend them.
Below are some links about how and why to buy a helmet. Hope you find it helpful.
Motorcycle Helmet Reviews from Best Motorcycle Gear
"How to Buy a Motorcycle Helmet," by Art Friedman
"Motorcycle Helmet Quiz: Check Your Head-Protection IQ," by Art Friedman
"Seven Flip-Face Motorcycle Helmets Compared," by Art Friedman
"Crash Padding - Part Two: Protecting Your Head," by David Hough
Snell Memorial Foundation [the last word on helmet safety]
Index of the Web.Com: Motorcycle Helmets
Dennis Kirk.Com (helmets and much more)
H&M Harley-Davidson.Com (Harley products on line)