They may look like Barbie's kidneys, but these chunks of custom molded, medical grade silicone are the best $75 I've ever spent on motorcycle gear.
I got mine in the marketplace area of last year's Red Bull MotoGP races at Mazda Laguna Seca Raceway, and the fitting process involved certified audiologist Marilyn Navia (who also sells them on (PlugUp.com) injecting warm goo into my ear canals, forming a mold from the crevices inside. Gross, I know. "You have pretty crooked ear canals," she remarked, which made sense since off-the-shelf earplugs always popped out easily.
The plugs reduce wind noise dramatically, which ultimately makes long road trips less fatiguing and potentially safer. I've even taken to wearing them on airplanes when I don't have room for my Bose QuietComfort noise cancelling headphones: these sound stoppers beat trying to tune out screaming babies, or worse, chatty passengers.
One note for motorcyclists: you'll want to check the rulebook of your local Department of Motor Vehicles, as some states limit their use.