Get some earplugs (squishy silicone work quite well). Put them on under some earmuffs. I like the Pro Ears (just get the cheap passive ones). It basically buys you 29-30dB from the plugs and maybe the same up to 33dB from the muffs, which is pretty good (as much as 35dB?).
If you want or will tolerate music (or background noise):
In Ear Monitors, ideally with custom made earmolds. Try a cheap pair first just to see if you're comfortable with the feeling of having earphones crammed in your ear canal, but if you like those, I'd strongly suggest getting custom earmolds made at an audiologist (maybe $200).
I have both Etymotics ER-4s and Logitech Ultimate Ears 6vi.
I wore them (underneath my electronic shooters muffs, sometimes, other times bare) on ranges with 14.5mm machine guns firing, as well as on helicopters, and they are awesome. Essentially 29-30dB earplugs and audiophile-grade headphones. As a plus, they're the size of a set of earbuds.
These are what professional musicians wear on stage.
The absolute best are the custom Ultimate Ears (well, there are 2-3 other great brands) -- they go up to about $1500. You can get what I have for $100-300, and those are also great.
+1 on the custom molded in ear monitors - usually have my iPod volume on the 2nd or 3rd bar (15%?) and that drowns out pretty much everything - crying babies on flights, annoying co-workers etc.
If no music is need / just silence - industrial foam plugs (30-33db attenuation) + gun-range ear muffs on top; and that should only cost about $25 in total too.
With foam plugs - many folks just stick them on top of the ear and think that's it - you have to squash them into a thin roll, quickly insert them into the ear so only about 1/3 of them sticks out. They expand in your ear in about 10-15secs, and are usually more than enough to dull out most annoying sounds.