I've used ear plugs as well, to lesser success. Many people are uncomfortable with the pressure it puts on their ears.

I've long been used to earplugs for a while (a couple years in a boarding school dorm necessitates them), but my ears just adapt to the lower noise level. I suppose the noise generator raises the noise floor, so external disturbing sounds have a lower SNR and thus you're less likely to react to them.

I find that my Sleep Phones (www.sleepphones.com) work pretty well without putting the pressure on my ears. The only problem is that the speakers in the headband can move, so you have to fiddle a little bit to get them over your ears.