I question the wisdom of using earplugs ever since the day I almost got hit by an ambulance while wearing headphones whose sound drowned out the sound of its siren. Besides, how can you keep Harley riders safe if you can't hear their loud pipes? :lol:
I got mine here:http://www.westone.com/earmold_styles.html
They used to have a model called MH-1. It is not on their website but they still make it with a different name and it fits great under the helmet, comfortable all day.
I've been using in ear monitors for over two years and wouldn't go without them.
Go read the entire thread that RAWIN2 cited. "Holy Sound Quality Batman". It is the most comprehensive discussion of custom ear buds and covers everything you need to know and how to approach the issue.
I bought custom ear molded plugs from Ear Plug Superstore with Challenger ear buds. Nice folks and they stand behind their product and work. Discuss your needs with them, as they can point you in the right direction.
Probably best to spend the 20 bucks or so and let an audioligst do the custom ear mold bit. You will be extremely pleased you made this move and wonder why you ever waited so long. You may have to sculpt the area in your helmet where your ears go, to give the ear buds just a little more room. Do buy the lubricant they sell for your ears.