I never wore ear plugs until about ten years ago and I, like a lot of others, regret not doing so from the age of 17. But then again, at that time, I rode a 350LC like a lunatic in DMs, jeans and a paddock jacket! Ear plugs just didn't enter the equation!
Since I became a little more responsible, I have had a couple of pairs of custom made motorcycle specific ear plugs; one set done by Ultimate Ear (�60 + �30 for impressions), and the other from Specsavers believe it or not (�120 including impressions). However, I have lost one plug from each pair! Here lies the main problem (other than cost) of custom ear plugs - it's very easy to lose a lot of money very quickly! But they are comfortable.
I now use the slightly more expensive universal ear plugs. They are a sort of louvred rubber or silicone design and have a solid core. They look a bit like this:
You can get them for between �10 - �20 a pair from loads of places on the web, substantially more than foam ones, but a lot less than custom. I've tried foam and custom and I found the above to be the best compromise between cost and effectiveness.
Although you can get this type of plug for different environments, I prefer the "musicians" versions to the "motorcyclists" version because they let a bit more ambient sound through (personal preference). Generally motorcycle plugs are about -30db and musician's plugs are around -20db.
Hope this helps? At the end of the day, any ear plug is better than none at all!