Have always maintained one of each (1/2, 3/4, full) for various riding conditions, length of rides/trips, different bikes (windscreen or not)...
Best half helmet I've ever own is my current, DOT approved, carbon fiber helmet. Smallest approved DOT helmet on the market, but I don't believe it's matched by any in strength or protection. They can be found at: http://www.carbonfiberhelmets.com/dot.htm Be sure to tour around their website, some useful info is posted.
As for my current 3/4 and full face, they are both HJC...first, I'm living less than 20 miles from their factory here in Korea, so the outlet and price is right. Second, the helmets actually fit very nicely and have numerous padding options that can be changed out to adjust the fit, plus they are removable and washable. My 3/4 Open face is an AC-3, great helmet, can be configured with a rachetable full face shield (in many shades, tints, or clear) or just worn with the visor and glasses/googles. It has opening/closing vents that really get some air flow into and out of the helmet. Full Face is the HJC SY-MAX with the flip-up/adjustable chin bar and ratcheting/changeable face shields. The face sheild changes on both the AC-3 and SY-MAX are tool-less, so we have numerous spare shields. The SY-MAX also has the removable, washable, fit determined pad and liners. The shells are actually one size and you can buy additional change out liners and pads. I've done that so I have spare helmets available for others. Simply do their fitting about 15 minutes before riding. Works out great, wife has both the AC-3 and SY-MAX also...plus her own bike. Keeps us from having a size assortment of helmets, especially with the pad kits so cheap. Keep the shiney side up- -Baron Stump