I don't use ear plugs but do use ear bud headphones that fit tightly in my ears when I go on long trips. They pretty much act as ear plugs. I can listen to my ipod on the lowest volume setting and still hear it fine, as well as passing traffic.
I don't use anything when I am just riding around, but if it is longer than an hour or two (especially on the highway) I use the ipod and ear buds (Skullcandy). I also have the iJet remote for my ipod so I can put it in a tank bag, or my pocket, and control it with the remote on my handlebars.
That said, I can't do any of this anymore since my ipod was stolen from my garage
