Hearing loss begins with a general loss of the high frequencies, but will also expose itself as dropouts in the midrange frequencies too, which hurts intelligibility. You don't need the highs that much, but you do need your midranges.
I HIGHLY recommend these plugs:
http://www.etymotic.com/ephp/er20.aspx
There are several varieties like it, but Etymotic is a very well respected audio company, and these plugs are only 12$. The only thing better is to get their custom fitted 'musicians' plugs, which have to be arranged through an audiologist. They cost around 150$, but they are perfectly fitted to your ear, and you can choose 9, 15, or 15 db of attenuation, based on your needs.
They have a very flat frequency response, an even 20db of attenuation across the entire band. They don't make things sound muffled, just quieter. A lot of musicians use them, because it doesn't screw up the sound of their instruments, and they are great for loud shows, since they don't make things sound bad, like foam plugs.
Protect that hearing, you only get one chance!
peace,
sam