I make no guarantees that the below are terrific vendors, only that they offer what appear to be quality items for a reasonable price. Many if not all of these items are probably available through your local dealers. Shop around for best pricing, the links are only examples.
Proficient Motorcycling: The ultimate book for riders
Helmet Ears: Have some fun while you're riding. Attach ears (or horns) to your helmet, $12
Heated Grip Kit: Aerostitch offers two models, one wraps 'over' your grips ($45) and acts sort of like a miniature electric blanket. The other mounts directly to the bars 'under' your grips ($27). Both provide lots of heat. You'll have to type "warm wrap grips" or "heated grip kit" into the Aerostitch search box to see the products.
BackAlign: It looks like a lifting belt but it's designed for motorcyclists to provide back support and encourage proper posture on long rides.
Helmet Fresh: When your helmet smells like a gym locker.
Boosteroo compact audio amplifier: Boosts volume of your portable mp3, disc players and radios.
Remove Before Flight ribbon: perfect reminder to remove your disk brake lock before trying to move.
Throttle Rocker: give your right wrist a break, $10
Helmet Holder: lock solutions $5 to $54
K&N Stock Replacement Air Filter: $54 Nomad & Classic Part #KA-1596
Emergency Tire Inflator: (C02 type)
Hydration System: for those long hot summer rides
Formotion Scooter Clocks & Thermometers: Mount on windshields or wherever.
CruzTools: Pocket Tool Set For Metric Bikes
Universal Vista Cruise: Throttle Lock
Back Off: Brake Light Flasher & Other Lighting Accessories..
Have more? Send them to Gadget for posting!