Some useful liniks from my personal favorite review site,
http://www.webbikeworld.com :
Helmet Reviews:
http://www.webbikeworld.com/motorcyc...le-helmets.htm
Size Chart w/ comparisons of different brands:
http://psndealer.com/dealersite/imag...ize_chart.html
Helmet FAQ:
http://www.webbikeworld.com/motorcyc...helmet-faq.htm
Helmet Weight chart:
http://www.webbikeworld.com/motorcyc...et-weights.htm
I've always purchased from
http://www.newenough.com. I've had nothing but great experiences from them. Their stuff generally runs a few bucks more than the cheapest available, but it's worth it for the customer service.
A few quick notes: HJC is the perennial budget helmet champion.. Joe Rocket helmets are made by HJC and use the same visors. Scorpion helmets have gained a lot of popularity in the last couple of years as a budget helmet that's good quality. KBC is generally considered to be on the low side of the quality scale. Arai and Shoei are some of the nicest and most comfortable helmets around, if you have the cash and find a good fit. Suomy is very nice stuff too, but is more oriented towards racing, which means lighter weight but less comfort and more helmet noise.
Fit is critical! Forget graphics and price points until you find a good fit. If you order online, make sure the site has a good return policy!
I have an HJC AC-11 right now, which gets the job done. I must have a strangely shaped head, because I've tried on every model from every company in every single MC store I've visited, and yet to find a good fit in another helmet that's an upgrade from the AC-11 (the Scorpion EX-300 & Joe Rocket RKT-101 are comfortable, but not as nice as my AC-11)
The most important thing I've learned is this: just because one helmet from a manufacturer fits you doesn't mean any other model will.
When the HJC AC-12 (successor to the AC-11) came out, I ordered one in a Medium, the same as my AC-11 thinking it would be a good replacement. The fit is totally different between the two, though, so now my roommate has a fancy new helmet, and I'm riding with my beat up old AC-11.